feat: Phase 6 export — writes Grav entry folders from Immich originals

Implements GET /export summary view and POST /export/run which downloads
originals from Immich, writes entry.md with YAML frontmatter, and sets
group status to exported. Includes POST /export/overwrite for single-group
re-export. All 42 tests pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/travel-memories/app/__init__.py

@@ -8,7 +8,7 @@ def create_app(state_dir=None, pages_dir=None):
     app.config["IMMICH_URL"] = os.environ.get("IMMICH_URL", "")
     app.config["IMMICH_API_KEY"] = os.environ.get("IMMICH_API_KEY", "")
 
-    from .routes import albums, triage, proxy, notes, nav, curate, group, write
+    from .routes import albums, triage, proxy, notes, nav, curate, group, write, export
     app.register_blueprint(albums.bp)
     app.register_blueprint(triage.bp)
     app.register_blueprint(proxy.bp)
@@ -17,6 +17,7 @@ def create_app(state_dir=None, pages_dir=None):
     app.register_blueprint(curate.bp)
     app.register_blueprint(group.bp)
     app.register_blueprint(write.bp)
+    app.register_blueprint(export.bp)
 
     @app.get("/health")
     def health():