feat(ui): one consistent navbar on every page (TODO.md L3)

frontend/assets/tuning.js

@@ -29,10 +29,10 @@
  *     the admin-only Sources link, and this page's own admin-only
  *     "Tuning" nav link (#nav-tuning), all decided by the module's
  *     cached whoami promise (exactly one /api/whoami request per
- *     page); plus the non-chat New chat binding — "new chat" means
- *     going to the chat, fresh (clear the phase-14 conversation key,
- *     then navigate to "/"), the same contract as sources.js /
- *     document.js.
+ *     page). Phase 34 task 02: the New chat binding is module-owned
+ *     (assets/header.js, the SINGLE one) — on a non-chat page "new
+ *     chat" means going to the chat, fresh (the module clears the
+ *     phase-14 conversation key and navigates to "/").
  *
  * Anonymous-safe (task 03): the header already hides the "Tuning" nav
  * link for anonymous visitors; a DIRECT anonymous URL still gets a safe
@@ -48,7 +48,7 @@
  * inlines it into the page bundle in the image build).
  */
 
-import { clearChatStorage, fetchIsAdmin, initSharedHeader } from "./header.js";
+import { fetchIsAdmin, initSharedHeader } from "./header.js";
 
 /* ---------- page elements (tuning.html, task 02) ---------- */
 const tuneForm = document.querySelector("#tune-form");
@@ -324,22 +324,14 @@ async function deleteNote(id, btn, li) {
   }
 }
 
-/* ---------- non-chat New chat + header boot (task 02) ---------- */
+/* ---------- header boot (task 02) ---------- */
 
-/* Phase 19 contract: New chat on a non-chat page means "go to the
- * chat, fresh": clear the phase-14 conversation key, then land on the
- * chat page — its empty state, since the conversation is gone from
- * storage (the same contract as sources.js / document.js). */
-const newChatBtn = document.querySelector("#new-chat-btn");
-if (newChatBtn) {
-  newChatBtn.addEventListener("click", () => {
-    clearChatStorage();
-    window.location.href = "/";
-  });
-}
-
-/* Boot: the shared header FIRST (Sign in/out + the admin-only nav
-   links — one cached whoami), then the note list — admin data only
+/* The New chat binding is module-owned (assets/header.js, phase 34
+ * task 02 — the SINGLE binding): on this non-chat page it clears the
+ * phase-14 conversation key and navigates to the chat's empty state.
+ *
+ * Boot: the shared header FIRST (Sign in/out + the admin-only nav
+ * links — one cached whoami), then the note list — admin data only
    (the Sources page gate pattern): an anonymous visitor gets the page
    frame with the empty state, and the create form 403s gracefully on
    submit if one tries. */