feat(plugin): admin-configurable marketplace URL as the install default

The Settings install command had a <your-scribe-repo> placeholder — not
copyable. Add an instance-global 'plugin_marketplace_url' setting (admin sets
it to the app's own repo) that every user's MCP Access reads, so the
/plugin marketplace add command is copyable out of the box. Keeps it universal
(each deployment configures its own repo) rather than hardcoding one.

- services/settings.get_admin_setting(key): admin-scoped global read.
- routes/plugin: GET /api/plugin/marketplace-url (any user) + PUT (admin).
- SettingsView: Admin → 'Plugin marketplace' field to set it; MCP Access
  marketplace field falls back to the configured value.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/views/SettingsView.vue

@@ -144,8 +144,16 @@ const claudeCodeCommand = computed(() => {
 const _MKT_KEY = 'plugin_marketplace_url';
 const pluginMarketplaceUrl = ref<string>(localStorage.getItem(_MKT_KEY) || '');
 watch(pluginMarketplaceUrl, (v) => localStorage.setItem(_MKT_KEY, (v || '').trim()));
+// Instance default, set by an admin (Admin tab) and loaded on mount. Used when
+// the per-browser field is blank so the install command is copyable out of the box.
+const serverMarketplaceUrl = ref('');
+const adminMarketplaceUrl = ref('');
+const savingMarketplaceUrl = ref(false);
+const marketplaceUrlSaved = ref(false);
 const pluginInstallCommands = computed(() => {
-  const mkt = (pluginMarketplaceUrl.value || '').trim() || '<your-scribe-repo>.git';
+  const mkt = (pluginMarketplaceUrl.value || '').trim()
+    || serverMarketplaceUrl.value
+    || '<your-scribe-repo>.git';
   return `/plugin marketplace add ${mkt}\n/plugin install scribe@scribe-plugin`;
 });
 
@@ -429,6 +437,17 @@ onMounted(async () => {
     searxngConfigured.value = false;
   }
 
+  // Plugin marketplace URL (instance default; readable by all users so the
+  // install command in MCP Access is copyable).
+  try {
+    const mk = await apiGet<{ marketplace_url: string }>("/api/plugin/marketplace-url");
+    serverMarketplaceUrl.value = mk.marketplace_url || "";
+    adminMarketplaceUrl.value = mk.marketplace_url || "";
+    if (!pluginMarketplaceUrl.value) pluginMarketplaceUrl.value = mk.marketplace_url || "";
+  } catch {
+    // not configured yet
+  }
+
   // Load admin settings
   if (authStore.isAdmin) {
     try {
@@ -658,6 +677,26 @@ async function saveBaseUrl() {
   }
 }
 
+async function saveMarketplaceUrl() {
+  savingMarketplaceUrl.value = true;
+  marketplaceUrlSaved.value = false;
+  try {
+    const url = adminMarketplaceUrl.value.trim();
+    await apiPut("/api/plugin/marketplace-url", { marketplace_url: url });
+    serverMarketplaceUrl.value = url;
+    // Reflect the new instance default in the copyable field unless the user
+    // set their own per-browser override.
+    if (!localStorage.getItem(_MKT_KEY)) pluginMarketplaceUrl.value = url;
+    marketplaceUrlSaved.value = true;
+    setTimeout(() => (marketplaceUrlSaved.value = false), 2000);
+  } catch (e) {
+    const body = (e as { body?: { error?: string } }).body;
+    toastStore.show(body?.error || "Failed to save marketplace URL", "error");
+  } finally {
+    savingMarketplaceUrl.value = false;
+  }
+}
+
 async function handleRestoreFile(event: Event) {
   const file = (event.target as HTMLInputElement).files?.[0];
   if (!file) return;
@@ -1663,6 +1702,31 @@ function formatUserDate(iso: string): string {
         </div>
       </section>
 
+      <section class="settings-section full-width">
+        <h2>Plugin marketplace</h2>
+        <p class="section-desc">
+          Git URL of the repo that ships this Scribe plugin (usually this app's own repo).
+          Shown to every user in <strong>MCP Access</strong> so the install command is
+          copyable. Example: https://git.example.com/you/Scribe.git
+        </p>
+        <div class="field url-field">
+          <label for="marketplace-url">Marketplace git URL</label>
+          <input
+            id="marketplace-url"
+            v-model="adminMarketplaceUrl"
+            type="url"
+            placeholder="https://git.example.com/you/Scribe.git"
+            class="input"
+          />
+        </div>
+        <div class="actions">
+          <button class="btn-save" @click="saveMarketplaceUrl" :disabled="savingMarketplaceUrl">
+            {{ savingMarketplaceUrl ? "Saving..." : "Save" }}
+          </button>
+          <span v-if="marketplaceUrlSaved" class="saved-msg">Saved!</span>
+        </div>
+      </section>
+
       <section class="settings-section full-width">
         <h2>Email / SMTP</h2>
         <p class="section-desc">Configure SMTP to enable email notifications for all users.</p>

src/scribe/routes/plugin.py

@@ -10,11 +10,17 @@ from __future__ import annotations
 
 from quart import Blueprint, g, jsonify, request
 
-from scribe.auth import login_required
+from scribe.auth import admin_required, get_current_user_id, login_required
 from scribe.services import plugin_context as plugin_ctx_svc
+from scribe.services.settings import get_admin_setting, set_setting
 
 plugin_bp = Blueprint("plugin", __name__, url_prefix="/api/plugin")
 
+# Setting key for the git URL of the marketplace that serves this plugin (the
+# Scribe app's own repo). Instance-global (stored on an admin account) so every
+# user's Settings page shows the real, copyable install command.
+_MARKETPLACE_KEY = "plugin_marketplace_url"
+
 
 @plugin_bp.get("/context")
 @login_required
@@ -30,3 +36,25 @@ async def session_context():
         project_id = 0
     result = await plugin_ctx_svc.build_session_context(g.user.id, project_id)
     return jsonify(result)
+
+
+@plugin_bp.get("/marketplace-url")
+@login_required
+async def get_marketplace_url():
+    """The plugin marketplace git URL, readable by any logged-in user so their
+    Settings page can show a copyable install command."""
+    return jsonify({"marketplace_url": await get_admin_setting(_MARKETPLACE_KEY)})
+
+
+@plugin_bp.put("/marketplace-url")
+@admin_required
+async def set_marketplace_url():
+    """Admin-set the marketplace git URL (e.g. this app's own repo)."""
+    data = await request.get_json() or {}
+    url = (data.get("marketplace_url") or "").strip()
+    if url:
+        scheme = url.split("://")[0].lower() if "://" in url else ""
+        if scheme not in ("http", "https"):
+            return jsonify({"error": "Marketplace URL must use http or https"}), 400
+    await set_setting(get_current_user_id(), _MARKETPLACE_KEY, url)
+    return jsonify({"status": "ok"})

src/scribe/services/settings.py

@@ -4,10 +4,28 @@ from sqlalchemy import delete as sa_delete, select
 
 from scribe.models import async_session
 from scribe.models.setting import Setting
+from scribe.models.user import User
 
 logger = logging.getLogger(__name__)
 
 
+async def get_admin_setting(key: str, default: str = "") -> str:
+    """Read an instance-global setting (one stored on an admin account).
+
+    Used for settings that aren't per-user — e.g. the plugin marketplace URL
+    shown to everyone in Settings. Mirrors the admin-scoped lookup used for
+    the application base URL.
+    """
+    async with async_session() as session:
+        result = await session.execute(
+            select(Setting)
+            .join(User, Setting.user_id == User.id)
+            .where(User.role == "admin", Setting.key == key)
+        )
+        setting = result.scalars().first()
+        return setting.value if setting and setting.value else default
+
+
 async def get_setting(user_id: int, key: str, default: str = "") -> str:
     async with async_session() as session:
         result = await session.execute(