Per-tool pages + multi-engine transcribe with expert controls

- Split monolithic index.php into per-tool pages (ask, search, summarize,
  timeline, redact, transcribe), each with its own URL and bookmarkable state
- Shared shell: includes/layout.php + layout_footer.php; shared form:
  includes/tool_form.php used by all text-tool pages
- index.php now redirects authenticated users to ask.php; unauthenticated
  users see the login gate only
- transcribe.php: engine selector (GPU/OpenAI/Azure), model size (small/
  medium/large-v3), diarize, language, expert settings (beam, VAD, task,
  initial prompt)
- api/transcribe.php: engine routing — GPU (cuttlefish), OpenAI BYOK,
  Azure AI Speech; passes model/beam/task/vad/prompt to Whisper server
- tools.js: data-active-tool body attr drives setTool() on load; <a> nav
  tabs skip click listeners; null guards on form/passcodeForm; engine radio
  toggle shows/hides BYOK key inputs and model selector; RTF shown in status
- tools.css: styles for BYOK inputs, expert settings panel, prompt textarea

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

assets/css/tools.css

@@ -1218,3 +1218,74 @@ p {
   gap: 0.5rem;
   margin-top: 0.75rem;
 }
+
+/* ── Transcribe extended controls ─────────────────────────────────────── */
+
+.byok-input {
+  font-size: 0.82rem;
+  padding: 0.3rem 0.6rem;
+  border: 1px solid var(--line);
+  border-radius: 6px;
+  background: var(--bg);
+  color: var(--ink);
+  width: 22rem;
+  max-width: 100%;
+}
+.byok-input--short { width: 9rem; }
+.byok-input:focus  { outline: 2px solid var(--teal); outline-offset: 1px; }
+
+.inline-hint {
+  font-size: 0.75rem;
+  color: var(--muted);
+  margin-left: 0.4rem;
+}
+
+.expert-settings {
+  border: 1px solid var(--line);
+  border-radius: 8px;
+  padding: 0;
+  margin-top: 0.75rem;
+}
+.expert-summary {
+  font-size: 0.82rem;
+  font-weight: 600;
+  color: var(--muted);
+  cursor: pointer;
+  padding: 0.55rem 0.9rem;
+  list-style: none;
+  user-select: none;
+}
+.expert-summary::-webkit-details-marker { display: none; }
+.expert-summary::before {
+  content: '▶ ';
+  font-size: 0.65rem;
+  transition: transform 0.15s;
+}
+.expert-settings[open] .expert-summary::before { content: '▼ '; }
+.expert-body {
+  padding: 0.6rem 0.9rem 0.9rem;
+  border-top: 1px solid var(--line);
+  display: flex;
+  flex-direction: column;
+  gap: 0.4rem;
+}
+.expert-field {
+  display: flex;
+  flex-direction: column;
+  gap: 0.25rem;
+  margin-top: 0.4rem;
+}
+.prompt-textarea {
+  font-size: 0.82rem;
+  padding: 0.4rem 0.6rem;
+  border: 1px solid var(--line);
+  border-radius: 6px;
+  background: var(--bg);
+  color: var(--ink);
+  resize: vertical;
+  width: 100%;
+  box-sizing: border-box;
+}
+.prompt-textarea:focus { outline: 2px solid var(--teal); outline-offset: 1px; }
+
+.control-hint { font-size: 0.74rem; color: var(--muted); font-weight: 400; }