feat(plugin): ship the Scribe Claude Code plugin in-repo (marketplace + plugin)

Per operator: the plugin lives in the app repo so it ships and versions in
lockstep with the app and the /api/plugin/context contract it targets (same
co-location rationale as the former in-repo MCP). A git-cloned marketplace
supports relative plugin sources, so the FabledScribe repo IS the marketplace.

- .claude-plugin/marketplace.json — source ./plugin
- plugin/.claude-plugin/plugin.json — userConfig (base URL, api key, project id)
- plugin/.mcp.json — http scribe server, ${user_config.*} substitution
- plugin/hooks/ — SessionStart push-channel hook (fail-open)
- plugin/skills/using-scribe — bootstrap skill
- plugin/README.md — install via the FabledScribe repo marketplace

Phase 2 of plan #755. Install/userConfig-substitution test pending.

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

plugin/hooks/hooks.json

@@ -0,0 +1,14 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "SCRIBE_URL=\"${user_config.api_endpoint}\" SCRIBE_TOKEN=\"${user_config.api_token}\" SCRIBE_PROJECT_ID=\"${user_config.project_id}\" bash \"${CLAUDE_PLUGIN_ROOT}/hooks/scribe_session_context.sh\""
+          }
+        ]
+      }
+    ]
+  }
+}

plugin/hooks/scribe_session_context.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Scribe plugin — SessionStart push channel.
+#
+# Curls the operator's Scribe instance for always-on rules + active-project
+# context and emits it as SessionStart `additionalContext`. Config comes from
+# plugin userConfig, passed in as env by hooks/hooks.json:
+#   SCRIBE_URL        base URL, no trailing slash (user_config.api_endpoint)
+#   SCRIBE_TOKEN      fmcp_ API key (user_config.api_token)
+#   SCRIBE_PROJECT_ID optional numeric project id (user_config.project_id)
+#
+# FAIL-OPEN: any missing tool/config, network error, or unreachable instance
+# injects nothing and exits 0. A session must never be blocked by Scribe.
+set -uo pipefail
+
+command -v jq   >/dev/null 2>&1 || exit 0
+command -v curl >/dev/null 2>&1 || exit 0
+
+url=${SCRIBE_URL:-}
+token=${SCRIBE_TOKEN:-}
+project_id=${SCRIBE_PROJECT_ID:-}
+[ -n "$url" ] && [ -n "$token" ] || exit 0
+
+q=""
+[ -n "$project_id" ] && q="?project_id=${project_id}"
+
+body=$(curl -fsS --max-time 8 \
+  -H "Authorization: Bearer ${token}" \
+  "${url%/}/api/plugin/context${q}" 2>/dev/null) || exit 0
+
+text=$(printf '%s' "$body" | jq -r '.context // empty' 2>/dev/null) || exit 0
+[ -n "$text" ] || exit 0
+
+jq -n --arg c "$text" \
+  '{hookSpecificOutput: {hookEventName: "SessionStart", additionalContext: $c}}'
+exit 0