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/models/notes.py

@@ -0,0 +1,37 @@
+from sqlalchemy import Column, Integer, String, Boolean, DateTime, Text, ForeignKey
+from sqlalchemy.orm import relationship
+from datetime import datetime, timezone
+from database import Base
+
+
+def _utcnow():
+    return datetime.now(timezone.utc)
+
+
+class SiteNote(Base):
+    __tablename__ = "site_notes"
+
+    id = Column(Integer, primary_key=True, index=True)
+    body = Column(Text, nullable=False)
+    created_by_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    created_at = Column(DateTime(timezone=True), default=_utcnow)
+    updated_at = Column(DateTime(timezone=True), default=_utcnow, onupdate=_utcnow)
+    is_pinned = Column(Boolean, default=False, nullable=False)
+
+    created_by = relationship("User", foreign_keys=[created_by_id])
+
+
+class SiteTodo(Base):
+    __tablename__ = "site_todos"
+
+    id = Column(Integer, primary_key=True, index=True)
+    body = Column(Text, nullable=False)
+    is_done = Column(Boolean, default=False, nullable=False)
+    done_at = Column(DateTime(timezone=True), nullable=True)
+    done_by_id = Column(Integer, ForeignKey("users.id"), nullable=True)
+    created_by_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    created_at = Column(DateTime(timezone=True), default=_utcnow)
+    priority = Column(String, default="normal", nullable=False)  # "normal" | "high"
+
+    created_by = relationship("User", foreign_keys=[created_by_id])
+    done_by = relationship("User", foreign_keys=[done_by_id])