[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/lib/ae_events/ae_events__event_file.ts

@@ -151,7 +151,7 @@ export async function load_ae_obj_li__event_file({
                     offset,
                     order_by_li,
                     try_cache,
-                    log_lvl: 2
+                    log_lvl: 0
                 });
                 return cached_li;
             }