[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/elements/element_manage_hosted_file_li.svelte

@@ -89,7 +89,7 @@
                     limit: 250,
                     // params: params,
                     try_cache: true,
-                    log_lvl: 2
+                    log_lvl: 0
                 });
 
                 // ae_tmp.show__file_li = false;
@@ -158,10 +158,6 @@
                                     slct_hosted_file_id = hosted_file_obj.hosted_file_id;
                                     slct_hosted_file_obj = hosted_file_obj;
                                 }
-                                log_lvl = 1;
-                                if (log_lvl) {
-                                    console.log(`slct_hosted_file_kv:`, slct_hosted_file_kv);
-                                }
                             }}
                             class="btn btn-sm preset-tonal-secondary hover:preset-filled-secondary-500"
                             title="Add/Remove file to/from the locally stored uploaded file list. This is referenced by other AE components."
@@ -195,7 +191,7 @@
                                         link_to_id: link_to_id,
                                         rm_orphan: true,
                                         fake_delete: false,
-                                        log_lvl: 1
+                                        log_lvl: 0
                                     });
                             }}
                             class:hidden={!$ae_loc.administrator_access}