DRY refactoring pass: shared mixins, route helpers, composables, CSS

Backend:
- models/base.py: TimestampMixin + CreatedAtMixin; applied to all 10+ models
- routes/utils.py: not_found() + parse_iso_date() helpers; used across all route files
- routes/milestones.py: _milestone_dict() helper replaces 5 repeated to_dict + progress blocks

Frontend:
- 5 new composables: useAutoSave, useEditorGuards, useTagSuggestions,
  useFloatingAssist, useListKeyboardNavigation
- ConfirmDialog.vue: reusable confirm modal replacing inline <teleport> blocks
- editor-shared.css: sidebar CSS consolidated from both editor views
- viewer-shared.css: context-bar/breadcrumb CSS consolidated from both viewer views
- NoteEditorView + TaskEditorView: ~120 lines each replaced with composable calls;
  duplicate scoped sidebar CSS removed
- NotesListView + TasksListView: inline keyboard-nav replaced with composable
- NoteViewerView + TaskViewerView: duplicate context-bar CSS removed

No behaviour changes. Net: -634 lines, +237 lines across 31 files.

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

src/fabledassistant/routes/milestones.py

@@ -4,6 +4,7 @@ import logging
 from quart import Blueprint, jsonify, request
 
 from fabledassistant.auth import login_required, get_current_user_id
+from fabledassistant.routes.utils import not_found
 from fabledassistant.services.milestones import (
     create_milestone,
     delete_milestone,
@@ -20,21 +21,22 @@ logger = logging.getLogger(__name__)
 milestones_bp = Blueprint("milestones", __name__, url_prefix="/api/projects")
 
 
+async def _milestone_dict(m) -> dict:
+    d = m.to_dict()
+    d.update(await get_milestone_progress(m.id))
+    return d
+
+
 @milestones_bp.route("/<int:project_id>/milestones", methods=["GET"])
 @login_required
 async def list_milestones_route(project_id: int):
     uid = get_current_user_id()
     project = await get_project(uid, project_id)
     if project is None:
-        return jsonify({"error": "Project not found"}), 404
+        return not_found("Project")
     status = request.args.get("status")
     milestones = await list_milestones(uid, project_id, status=status)
-    result = []
-    for m in milestones:
-        entry = m.to_dict()
-        progress = await get_milestone_progress(m.id)
-        entry.update(progress)
-        result.append(entry)
+    result = [await _milestone_dict(m) for m in milestones]
     return jsonify({"milestones": result})
 
 
@@ -44,7 +46,7 @@ async def create_milestone_route(project_id: int):
     uid = get_current_user_id()
     project = await get_project(uid, project_id)
     if project is None:
-        return jsonify({"error": "Project not found"}), 404
+        return not_found("Project")
     data = await request.get_json()
     if not data.get("title"):
         return jsonify({"error": "title is required"}), 400
@@ -55,9 +57,7 @@ async def create_milestone_route(project_id: int):
         description=data.get("description"),
         order_index=data.get("order_index", 0),
     )
-    entry = milestone.to_dict()
-    entry.update(await get_milestone_progress(milestone.id))
-    return jsonify(entry), 201
+    return jsonify(await _milestone_dict(milestone)), 201
 
 
 @milestones_bp.route("/<int:project_id>/milestones/<int:milestone_id>", methods=["GET"])
@@ -66,10 +66,8 @@ async def get_milestone_route(project_id: int, milestone_id: int):
     uid = get_current_user_id()
     milestone = await get_milestone(uid, milestone_id)
     if milestone is None or milestone.project_id != project_id:
-        return jsonify({"error": "Milestone not found"}), 404
-    entry = milestone.to_dict()
-    entry.update(await get_milestone_progress(milestone.id))
-    return jsonify(entry)
+        return not_found("Milestone")
+    return jsonify(await _milestone_dict(milestone))
 
 
 @milestones_bp.route("/<int:project_id>/milestones/<int:milestone_id>", methods=["PATCH"])
@@ -78,16 +76,14 @@ async def update_milestone_route(project_id: int, milestone_id: int):
     uid = get_current_user_id()
     milestone = await get_milestone(uid, milestone_id)
     if milestone is None or milestone.project_id != project_id:
-        return jsonify({"error": "Milestone not found"}), 404
+        return not_found("Milestone")
     data = await request.get_json()
     allowed = {"title", "description", "status", "order_index"}
     fields = {k: v for k, v in data.items() if k in allowed}
     updated = await update_milestone(uid, milestone_id, **fields)
     if updated is None:
-        return jsonify({"error": "Milestone not found"}), 404
-    entry = updated.to_dict()
-    entry.update(await get_milestone_progress(updated.id))
-    return jsonify(entry)
+        return not_found("Milestone")
+    return jsonify(await _milestone_dict(updated))
 
 
 @milestones_bp.route("/<int:project_id>/milestones/<int:milestone_id>", methods=["DELETE"])
@@ -96,10 +92,10 @@ async def delete_milestone_route(project_id: int, milestone_id: int):
     uid = get_current_user_id()
     milestone = await get_milestone(uid, milestone_id)
     if milestone is None or milestone.project_id != project_id:
-        return jsonify({"error": "Milestone not found"}), 404
+        return not_found("Milestone")
     deleted = await delete_milestone(uid, milestone_id)
     if not deleted:
-        return jsonify({"error": "Milestone not found"}), 404
+        return not_found("Milestone")
     return "", 204
 
 
@@ -109,7 +105,7 @@ async def get_milestone_tasks_route(project_id: int, milestone_id: int):
     uid = get_current_user_id()
     milestone = await get_milestone(uid, milestone_id)
     if milestone is None or milestone.project_id != project_id:
-        return jsonify({"error": "Milestone not found"}), 404
+        return not_found("Milestone")
     status_filter = request.args.get("status")
     limit = min(request.args.get("limit", 100, type=int), 500)
     offset = request.args.get("offset", 0, type=int)