refactor: DRY pass on backend — pagination helper and sharing utilities

- Add parse_pagination() to routes/utils.py; replace 6 duplicate limit/offset extractions in notes, tasks, chat, projects, milestones routes
- Extract _enrich_shares() in sharing.py; eliminates identical 12-line loop in list_project_shares and list_note_shares
- Extract _deduplicate_by_permission() in sharing.py; eliminates identical deduplication blocks in list_shared_with_me for projects and notes

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

src/fabledassistant/routes/notes.py

@@ -7,7 +7,7 @@ from fabledassistant.services.embeddings import upsert_note_embedding
 from quart import Blueprint, Response, jsonify, request
 
 from fabledassistant.auth import login_required, get_current_user_id
-from fabledassistant.routes.utils import not_found, parse_iso_date
+from fabledassistant.routes.utils import not_found, parse_iso_date, parse_pagination
 from fabledassistant.config import Config
 from fabledassistant.services.assist import build_assist_messages
 from fabledassistant.services.generation_buffer import (
@@ -49,8 +49,7 @@ async def list_notes_route():
     tag = request.args.getlist("tag")
     sort = request.args.get("sort", "updated_at")
     order = request.args.get("order", "desc")
-    limit = min(request.args.get("limit", 50, type=int), 500)
-    offset = request.args.get("offset", 0, type=int)
+    limit, offset = parse_pagination()
 
     # Default to non-task notes only; ?is_task=true for tasks, ?all=true for everything
     is_task: bool | None = False