feat: add base shell, notes panel, back-navigation with stale propagation

Implements Task 4: base.html DaisyUI/Alpine shell, notes autosave panel,
nav.py phase switching with downstream stale marking, notes.py save/get
endpoints, state debug endpoint, and stub /triage route for test support.

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

services/travel-memories/app/routes/notes.py

@@ -1,3 +1,25 @@
-from flask import Blueprint
+from flask import Blueprint, current_app, jsonify, request
+from app.state import load_state, save_state
 
 bp = Blueprint("notes", __name__)
+
+PHASE_ORDER = ["triage", "curate", "group", "write", "export"]
+
+
+@bp.post("/notes/save")
+def save_notes():
+    body = request.get_json()
+    state = load_state(body["album_id"], current_app)
+    if state is None:
+        return jsonify({"error": "no state"}), 404
+    state.notes = body["notes"]
+    save_state(state, current_app)
+    return jsonify({"ok": True})
+
+
+@bp.get("/notes/<album_id>")
+def get_notes(album_id):
+    state = load_state(album_id, current_app)
+    if state is None:
+        return jsonify({"error": "no state"}), 404
+    return jsonify({"notes": state.notes})