feat: Implement Micropub endpoint for creating posts (Phase 3)

Following design in /docs/design/micropub-endpoint-design.md and
/docs/decisions/ADR-028-micropub-implementation.md

Micropub Module (starpunk/micropub.py):
- Property normalization for form-encoded and JSON requests
- Content/title/tags extraction from Micropub properties
- Bearer token extraction from Authorization header or form
- Create action handler integrating with notes.py CRUD
- Query endpoints (config, source, syndicate-to)
- OAuth 2.0 compliant error responses

Micropub Route (starpunk/routes/micropub.py):
- Main /micropub endpoint handling GET and POST
- Bearer token authentication and validation
- Content-type handling (form-encoded and JSON)
- Action routing (create supported, update/delete return V1 error)
- Comprehensive error handling

Integration:
- Registered micropub blueprint in routes/__init__.py
- Maps Micropub properties to StarPunk note format
- Returns 201 Created with Location header per spec
- V1 limitations clearly documented (no update/delete)

All 23 Phase 3 tests pass
Total: 77 tests pass (21 Phase 1 + 33 Phase 2 + 23 Phase 3)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

starpunk/routes/__init__.py

@@ -7,7 +7,7 @@ admin, auth, and (conditionally) dev auth routes.
 
 from flask import Flask
 
-from starpunk.routes import admin, auth, public
+from starpunk.routes import admin, auth, micropub, public
 
 
 def register_routes(app: Flask) -> None:
@@ -19,7 +19,8 @@ def register_routes(app: Flask) -> None:
 
     Registers:
         - Public routes (homepage, note permalinks)
-        - Auth routes (login, callback, logout)
+        - Auth routes (login, callback, logout, token, authorization)
+        - Micropub routes (Micropub API endpoint)
         - Admin routes (dashboard, note management)
         - Dev auth routes (if DEV_MODE enabled)
     """
@@ -29,6 +30,9 @@ def register_routes(app: Flask) -> None:
     # Register auth routes
     app.register_blueprint(auth.bp)
 
+    # Register Micropub routes
+    app.register_blueprint(micropub.bp)
+
     # Register admin routes
     app.register_blueprint(admin.bp)