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/Models/DailyNoteEntity.cs

@@ -6,5 +6,9 @@ public sealed class DailyNoteEntity
     public DateOnly Date { get; set; }
     public string Text { get; set; } = string.Empty;
     public int SortOrder { get; set; }
+
+    /// <summary>True when an agent wrote this note through the MCP tool rather than the user.
+    /// Drives the UI marker and the per-day cap in <c>NotesMcpTools</c>.</summary>
+    public bool FromAgent { get; set; }
     public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
 }