feat(persona-chat): continue an SMS thread with a persona

Persona conversations can now be anchored on a message in an SMS thread.
Creating one snapshots the thread up to that message (via SMS-API) into the
row; every turn appends it to the persona prompt with guidance to talk like a
text thread rather than write an insight.

Anchored turns get four tools: get_thread_messages (page the thread),
look_at_message_image (local vision on an MMS photo), get_photos_near_time
(library photos with tags and people) and look_at_photo (local vision on a
library photo). The conversation list filters by contact_id.

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

src/database/schema.rs

@@ -197,6 +197,11 @@ diesel::table! {
         turn_count -> Integer,
         created_at -> BigInt,
         updated_at -> BigInt,
+        anchor_contact_id -> Nullable<BigInt>,
+        anchor_contact_name -> Nullable<Text>,
+        anchor_message_id -> Nullable<BigInt>,
+        anchor_ts -> Nullable<BigInt>,
+        anchor_context -> Nullable<Text>,
     }
 }