feat(family): platforms declared at inception and detected from bound repos (milestone 463 step 2, #4988)

A project's platforms decide which family ideas reach it. This step makes membership answerable from every door:

- services/platforms.py: the global catalog (writes are admin-only and duplicate-gated by slug); pure marker detection; and membership reads and writes. Detection only ADDS, and only where nobody has answered. It never overrides a declared or rejected row and never removes one.
- coverage: the archive scan now carries every path, and the refresh runs detection fail-open.
- inception: a platforms choice (slugs, or null for unanswered). The list is the whole answer: members left out of it become rejected.
- MCP: list_platforms and set_project_platforms; enter_project and get_project carry the project's platforms.
- REST: /api/platforms (admin writes) and /api/projects/<id>/platforms.
- UI: a platforms checklist on the inception card, a Family tab on ProjectView, and a Platforms admin tab in Settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scribe/routes/platforms.py

@@ -0,0 +1,96 @@
+"""Platform routes — the GLOBAL platform catalog, and which platforms a
+project is (milestone 463 step 2).
+
+Two shapes, as with the canonical areas:
+
+- `/api/platforms` — the catalog. Readable by any signed-in user; writable
+  only by an admin, since a vocabulary anyone extends stops being shared.
+- `/api/projects/<id>/platforms` — a project's answers, authorised by the
+  PROJECT (read to see them, write to change them). The service enforces
+  both; these are thin wrappers.
+"""
+import logging
+
+from quart import Blueprint, jsonify, request
+
+from scribe.auth import admin_required, get_current_user_id, login_required
+from scribe.routes.utils import not_found
+from scribe.services import platforms as platforms_svc
+
+logger = logging.getLogger(__name__)
+
+platforms_bp = Blueprint("platforms", __name__, url_prefix="/api")
+
+_EDITABLE = ("name", "description", "order_index", "markers")
+
+
+@platforms_bp.route("/platforms", methods=["GET"])
+@login_required
+async def list_platforms_route():
+    entries = await platforms_svc.list_platforms()
+    return jsonify({"platforms": [e.to_dict() for e in entries]})
+
+
+@platforms_bp.route("/platforms", methods=["POST"])
+@admin_required
+async def create_platform_route():
+    uid = get_current_user_id()
+    data = await request.get_json() or {}
+    if not (data.get("name") or "").strip():
+        return jsonify({"error": "name is required"}), 400
+    try:
+        entry = await platforms_svc.create_platform(
+            uid, data["name"], description=data.get("description"),
+            markers=data.get("markers"),
+        )
+    except ValueError as exc:
+        return jsonify({"error": str(exc)}), 400
+    if entry is None:
+        return jsonify({"error": "Permission denied"}), 403
+    # Duplicate-gated on the slug: the entry that already is this platform
+    # comes back as a 409 rather than a second spelling of it.
+    if isinstance(entry, dict):
+        return jsonify(entry), 409
+    return jsonify(entry.to_dict()), 201
+
+
+@platforms_bp.route("/platforms/<int:platform_id>", methods=["PATCH"])
+@admin_required
+async def update_platform_route(platform_id: int):
+    uid = get_current_user_id()
+    data = await request.get_json() or {}
+    fields = {k: v for k, v in data.items() if k in _EDITABLE}
+    try:
+        entry = await platforms_svc.update_platform(uid, platform_id, **fields)
+    except ValueError as exc:
+        return jsonify({"error": str(exc)}), 400
+    if entry is None:
+        return not_found("Platform")
+    return jsonify(entry.to_dict())
+
+
+@platforms_bp.route("/projects/<int:project_id>/platforms", methods=["GET"])
+@login_required
+async def project_platforms_route(project_id: int):
+    """Every platform the project has an answer for — rejected included, so
+    a screen can show "no" as well as "yes"."""
+    rows = await platforms_svc.project_platforms(get_current_user_id(), project_id)
+    if rows is None:
+        return not_found("Project")
+    return jsonify({"project_platforms": rows})
+
+
+@platforms_bp.route("/projects/<int:project_id>/platforms", methods=["PUT"])
+@login_required
+async def set_project_platforms_route(project_id: int):
+    """Body: {"platforms": {<slug>: "declared" | "rejected" | null}}. Only
+    the slugs named change; null withdraws the answer. Applies whole or not
+    at all."""
+    data = await request.get_json() or {}
+    try:
+        rows = await platforms_svc.set_project_platforms(
+            get_current_user_id(), project_id, data.get("platforms"),
+        )
+    except ValueError as exc:
+        return jsonify({"error": str(exc)}), 400
+    return jsonify({"project_platforms": rows})