feat(notes): add_note MCP tool with a per-day agent cap

Agents can write into the user's daily notes, but only within limits:
max 10 agent notes a day, max 500 characters, add only — no edit, no
delete. A new from_agent column separates their lines from the user's
so the cap counts the right ones and the UI can mark them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/ClaudeDo.Data/Repositories/DailyNoteRepository.cs

@@ -22,7 +22,13 @@ public sealed class DailyNoteRepository
             .OrderBy(n => n.Date).ThenBy(n => n.SortOrder)
             .ToListAsync(ct);
 
-    public async Task<DailyNoteEntity> AddAsync(DateOnly day, string text, CancellationToken ct = default)
+    /// <summary>Notes an agent wrote on <paramref name="day"/> — the number the MCP cap counts against.</summary>
+    public async Task<int> CountAgentNotesAsync(DateOnly day, CancellationToken ct = default) =>
+        await _context.DailyNotes.AsNoTracking()
+            .CountAsync(n => n.Date == day && n.FromAgent, ct);
+
+    public async Task<DailyNoteEntity> AddAsync(
+        DateOnly day, string text, bool fromAgent = false, CancellationToken ct = default)
     {
         var nextOrder = await _context.DailyNotes
             .Where(n => n.Date == day)
@@ -34,6 +40,7 @@ public sealed class DailyNoteRepository
             Date = day,
             Text = text,
             SortOrder = nextOrder + 1,
+            FromAgent = fromAgent,
             CreatedAt = DateTime.UtcNow,
         };
         _context.DailyNotes.Add(note);