feat: Phase 2C — notes & todos

- New models: SiteNote, SiteTodo (site_notes, site_todos tables)
- New schemas: NoteOut, TodoOut with creator/done-by name enrichment
- New router: /api/notes/ — full CRUD for notes and todos
  - Notes: create, list (pinned first), update (body + pin), delete
  - Todos: create, list (undone high-priority first), toggle done, edit, delete
  - Marking done records done_at + done_by_id; unchecking clears both
- Migrations: CREATE TABLE IF NOT EXISTS for both tables (additive, safe)
- NotesPage.jsx: two-column layout — notes left, todos right
  - Notes: inline click-to-edit, pin toggle, Ctrl+Enter to save, pinned section on top
  - Todos: inline edit, high-priority flag, completed collapse toggle
- /notes route added to App.jsx
- NotebookPen sidebar entry between Διαχείριση and Ρυθμίσεις

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

local_backend/schemas/notes.py

@@ -0,0 +1,51 @@
+from pydantic import BaseModel
+from typing import Optional
+from datetime import datetime
+
+
+class NoteCreate(BaseModel):
+    body: str
+    is_pinned: bool = False
+
+
+class NoteUpdate(BaseModel):
+    body: Optional[str] = None
+    is_pinned: Optional[bool] = None
+
+
+class NoteOut(BaseModel):
+    id: int
+    body: str
+    is_pinned: bool
+    created_by_id: int
+    created_by_name: Optional[str] = None
+    created_at: datetime
+    updated_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class TodoCreate(BaseModel):
+    body: str
+    priority: str = "normal"
+
+
+class TodoUpdate(BaseModel):
+    body: Optional[str] = None
+    priority: Optional[str] = None
+    is_done: Optional[bool] = None
+
+
+class TodoOut(BaseModel):
+    id: int
+    body: str
+    is_done: bool
+    done_at: Optional[datetime] = None
+    done_by_id: Optional[int] = None
+    done_by_name: Optional[str] = None
+    created_by_id: int
+    created_by_name: Optional[str] = None
+    created_at: datetime
+    priority: str
+
+    model_config = {"from_attributes": True}