fix(persona-chat): review fixes before merge

- Thread tools are bound server-side to the chat's own thread. The model
  used to pass contact_id, so practice mode could read any conversation it
  named; a model-supplied contact_id is now only checked, never trusted, and
  the prompts no longer hand it one.
- Practice chats need no persona. They're stored under PRACTICE_PERSONA_ID
  and run with an inert stand-in, so deleting or editing personas can't hide
  or break them. persona_id is optional on create for as_contact.
- The per-thread list filters in SQL (list_persona_chats_for_contact, served
  by idx_persona_chat_anchor_contact) instead of decoding every transcript.
- fetch_mms_image checks the content type and a 20 MB cap before reading
  the body, so a video attachment isn't downloaded in full.
- get_photos_near_time unions tags over every path sharing the content, per
  the multi-library model.
- look_at_photo only opens indexed photos, so an excluded folder can't be
  read by guessing a path.
- One date parser: get_photos_near_time uses date_info::parse_center.
- Practice prompt source rewrapped.

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

src/ai/insight_chat.rs

@@ -473,6 +473,7 @@ impl InsightChatService {
                             &normalized,
                             req.user_id,
                             &active_persona,
+                            None,
                         )
                         .instrument(loop_span.clone())
                         .await;
@@ -1435,6 +1436,7 @@ impl InsightChatService {
             normalized,
             user_id,
             active_persona,
+            None,
             max_iterations,
             entry,
             fitter,
@@ -1990,6 +1992,7 @@ impl InsightChatService {
                             normalized,
                             user_id,
                             active_persona,
+                            None,
                         )
                         .await;
                     let (result_preview, result_truncated) = truncate_tool_result(&result);
@@ -2624,6 +2627,7 @@ pub async fn run_streaming_agentic_loop_with_entry(
     normalized: &str,
     user_id: i32,
     active_persona: &str,
+    thread_contact: Option<i64>,
     max_iterations: usize,
     entry: &Arc<TurnEntry>,
     fitter: &mut ContextFitter,
@@ -2720,6 +2724,7 @@ pub async fn run_streaming_agentic_loop_with_entry(
                             normalized,
                             user_id,
                             active_persona,
+                            thread_contact,
                         )
                         .await
                 } else {