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>

includes/layout_footer.php

@@ -0,0 +1,22 @@
+        </section><!-- /tool-panel -->
+
+        <aside class="reasoning-panel" aria-labelledby="reasoningTitle">
+            <div class="reasoning-head">
+                <p class="eyebrow">Evidence trail</p>
+                <h2 id="reasoningTitle">Reasoning</h2>
+            </div>
+            <ol id="traceList" class="trace-list">
+                <li>
+                    <span class="trace-status waiting"></span>
+                    <div>
+                        <strong>Waiting</strong>
+                        <p>Run a tool to see interpretation, retrieval, confidence, uncertainty, and next step.</p>
+                    </div>
+                </li>
+            </ol>
+        </aside>
+    </section><!-- /workspace -->
+</main><!-- /appShell -->
+<script src="assets/js/tools.js" defer></script>
+</body>
+</html>