fix: reduce svelte-check warnings from 175 to 95 (80 eliminated)

Svelte 5 reactivity pattern fixes:
- Convert prop/data captures to $derived where used in reactive contexts
- Wrap store assignments in $effect + untrack for ae_acct pattern
- Move sign_in_out URL param processing to onMount (from top-level if(browser))
- Wrap debug console.log blocks in $effect instead of top-level if(log_lvl)
- Fix $state initializers reading props directly ($state(link_to_id) → $state(''))
- Fix box = $state(null) in journals layout

CSS fixes:
- TipTap scss: change :global(.tiptap){nested} to :global{.tiptap{nested}} so
  Svelte does not scope-hash dynamic content selectors (latent CSS bug fixed)
- element_manage_hosted/event: dq__where vars → $derived for reactive liveQuery

Config:
- svelte.config.js: add onwarn (suppresses a11y/CSS in Vite pipeline; note:
  svelte-check 4.x does not read onwarn so CLI count unchanged)

Remaining 95 warnings (acceptable baseline):
- 70x a11y_label: form labels need for/id attributes (proper a11y fix deferred)
- 12x lu_* false positives in IDAA async callbacks (correct code)
- 8x CSS dynamic selectors Svelte cannot detect at compile time
- 5x other intentional patterns (autofocus, form state, log_lvl callbacks)

src/routes/events/[event_id]/sign_in_out.svelte

@@ -14,7 +14,7 @@
         lq__auth__event_presenter_obj
     }: Props = $props();
 
-    import { browser } from '$app/environment';
+    import { onMount } from 'svelte';
     import { goto } from '$app/navigation';
 
     import {
@@ -34,7 +34,7 @@
         events_trig_kv
     } from '$lib/stores/ae_events_stores';
 
-    if (browser) {
+    onMount(() => {
         console.log('Browser environment detected.');
 
         console.log(
@@ -98,7 +98,7 @@
             // We need to set browser history and force all load functions to rerun.
             goto(new_url, { replaceState: true, invalidateAll: true });
         }
-    }
+    });
 
     // For session point of contact (moderator, chair, LCI Champions).
     function session_sign_in() {