feat(persona-chat): practice mode — play the contact

An anchored conversation now has a mode. 'about' is the existing behaviour (a
persona talks with the user about the thread). 'as_contact' has the model play
the contact so the user can rehearse the conversation: its own prompt (stay in
the contact's voice, don't invent facts, coach on 'out of character'), no
persona prompt, and only the thread tools — no memory, library, calendar or
other-thread access, and no knowledge writes.

The shared persona/file-chat loop now refuses tool calls that weren't in the
turn's catalog, so the gates hold even when a model names a tool it wasn't
offered.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/database/mod.rs

@@ -64,7 +64,9 @@ pub use knowledge_dao::{
     KnowledgeDao, PersonaFilter, RecentActivity, SqliteKnowledgeDao,
 };
 pub use location_dao::{LocationHistoryDao, SqliteLocationHistoryDao};
-pub use persona_dao::{ImportPersona, PersonaDao, PersonaPatch, SmsAnchor, SqlitePersonaDao};
+pub use persona_dao::{
+    AnchorMode, ImportPersona, PersonaDao, PersonaPatch, SmsAnchor, SqlitePersonaDao,
+};
 pub use precomputed_reel_dao::{PrecomputedReelDao, SqlitePrecomputedReelDao};
 pub use preview_dao::{PreviewDao, SqlitePreviewDao};
 pub use search_dao::{SearchHistoryDao, SqliteSearchHistoryDao};