[Perf] Fix liveQuery reactivity, silence debug logs, add performance guidelines

- launcher/+layout.svelte: convert lq__event_session_obj from $derived to
  $derived.by() so Svelte tracks event_session_id as a dependency; the old
  pattern read the store inside the Dexie async callback where Svelte's
  tracking is off, so the liveQuery never updated on session change
- ae_events__event_file.ts: fix hardcoded log_lvl: 2 in SWR fire-and-forget
  background refresh (always-on debug logging on every cache hit) → 0
- e_app_sign_in_out.svelte: lower 6 call-site log levels (1×log_lvl:2,
  5×log_lvl:1) to 0; sign-in runs on every page load
- element_manage_hosted_file_li.svelte: log_lvl:2 → 0 in refresh call;
  remove log_lvl=1 assignment + debug block inside click handler; log_lvl:1
  → 0 in delete call
- AE__Performance_Guidelines.md: add 5 Svelte 5 runes rules covering
  $derived.by() for reactive liveQuery, liveQuery purity, cheap equality
  guards ($id+updated_on, ID-join, shallow_equal), untrack() requirement,
  and log_lvl discipline

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/routes/events/[event_id]/(launcher)/launcher/+layout.svelte

@@ -222,9 +222,12 @@
     });
 
     // Event Session (Main View Trigger - Needed for Global Header/Idle)
-    let lq__event_session_obj = $derived(
-        liveQuery(() => db_events.session.get($events_slct.event_session_id))
-    );
+    // $derived.by: capture ID in outer closure so Svelte tracks it as a dependency.
+    // liveQuery callback runs in Dexie's async context where Svelte tracking is off.
+    let lq__event_session_obj = $derived.by(() => {
+        const id = $events_slct.event_session_id;
+        return liveQuery(() => db_events.session.get(id));
+    });
 
     // Store sync effects — keep liveQuery closures pure (data-only) and sync to
     // $events_slct here in reactive effects instead. Comparing updated_on + id is