feat(badges): search filter polish and result limit stepper

- Replace show_hidden checkbox with visibility_filter select (Default /
  Show Hidden / Show Disabled+Hidden) — collapses two orphaned boolean
  fields (show_hidden, show_not_enabled) into one purpose-built value;
  wires disabled-badge filter through to both IDB and API paths
- Add max-results stepper (edit mode only): steps of 25 up to 250,
  steps of 100 up to 2550; tier-capped (trusted=250, manager=2550);
  stepper uses pure reactivity — no handle_search_trigger() call needed
- Fix fallback liveQuery (SCENARIO 2): was hardcoded .limit(50);
  now reads qry_result_limit in outer $derived.by so Svelte tracks it
  and stepper updates the no-text browse list immediately
- Fix Search button disabled state: replace pointer-events-none +
  class:opacity-50 with HTML disabled attribute + disabled:cursor-not-allowed
  so hover cursor reflects disabled state correctly
- Global placeholder fix (app.css): add italic + opacity-0.6 rule for
  .input/.textarea ::placeholder in light mode; add italic to dark rule —
  prevents placeholder text from reading as typed content

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

src/app.css

@@ -163,9 +163,16 @@ html.light {
     background-color: rgb(55 65 81); /* gray-700 */
     border-color: rgb(75 85 99); /* gray-600 */
 }
+.input::placeholder,
+.textarea::placeholder {
+    font-style: italic;
+    opacity: 0.6;
+}
 .dark .input::placeholder,
 .dark .textarea::placeholder {
-    color: rgb(156 163 175); /* gray-400 — legible at reduced opacity */
+    color: rgb(156 163 175); /* gray-400 */
+    font-style: italic;
+    opacity: 0.8; /* gray-400 is already dim; subtle additional fade */
 }
 /* Option elements in dark selects — forces browser native dark chrome */
 .dark .select option {