feat(brand): configurable app name — BOR_APP_NAME drives /api/config + the frontend brand layer

One env var (BOR_APP_NAME, default "Brain of Reese") now drives the app's
display name everywhere (TODO.md L12 — owner ask: "a way to customize the
name for 'Brain of'. Should be an env var."). The existing app_name setting
is the source of truth (phase locked decision — no new variable, no rename);
with the variable unset the app is byte-identical to before.

Endpoint (A10 public/stateless, no secrets):
  GET /api/config → exactly {app_name, version} (app/api/config.py, the
  health.py pattern; registered before the static mount). Integration tests:
  anonymous 200, default values, a Settings override follows, key set is
  exactly two keys — no other setting may leak in later.

Frontend brand layer (A11 — runtime fetch, static templates stay static):
  assets/brand.js — a CLASSIC script, first on all six pages, so its top
  level runs at parse time: window.BOR_BRAND = "Brain of Reese"
  synchronously (the default renders immediately, no blank flash), then a
  no-store fetch of /api/config applies the name — document.title (global
  replace), every .brand-text (a name starting "Brain of " keeps the bold
  split Brain of <strong>rest</strong>, any other name renders plain; the
  operator-controlled name is HTML-escaped before innerHTML), a TreeWalker
  over text nodes (script/style rejected — page source never rewritten),
  and the aria-label/placeholder/meta-content attributes. Fetch failure
  keeps the default + console.warn (the loadHealth house style).
  app.js (status labels, typing label, elapsed-hint aria, tool labels) and
  document.js (viewer titles) read window.BOR_BRAND at CALL time via
  brand() — a label set after the fetch lands carries the configured name.
  Containerfile: esbuild minify line for brand.js (classic, like markdown.js);
  the phase-33 ?v= cache-busting picks the new asset ref up automatically.

E2E (A16 — one story, one file, isolated): test_configurable_brand.py boots
a SECOND app instance (same DB/mock-LLM/admin-auth env block, port APP_PORT+1,
BOR_APP_NAME="Brain of Testy") — the shared conftest server keeps the
default name so every other suite's title/label assertions stay untouched —
and asserts /api/config on both instances, the index title/brand/greeting/
#messages aria-label, the sources + login page titles, and one pre-token
chat turn (think out loud marker) whose #send-status reads "Brain of Testy
is thinking"; the no-op regression pins the shared server's default bytes.

Docs: .env.example App section + README configuration reference — what it
affects (titles, header brand, status labels, aria text), the default, the
bold-split rendering rule.

Gates: 695 unit+integration passed, app/ coverage 99% (>90%), story E2E
green in isolation (two consecutive runs), brand-string suites (smoke,
shared header, header consistency, chat persistence) green, ruff + pyright
clean.

frontend/assets/app.js

@@ -47,8 +47,9 @@
  * "thinking": the UI state itself stays "thinking" (button stays
  * disabled — never stale, PLAN §7.4) while the LABELS change — the
  * button says "Calling tool…", the #send-status + typing-indicator
- * labels say what Brain is doing ("Brain of Reese is listing documents"
- * / "Brain of Reese is reading source/path"), and a visible `.tool-call`
+ * labels say what Brain is doing ("…is listing documents" /
+ * "…is reading source/path" — the name prefix resolves from
+ * window.BOR_BRAND at call time, phase 39), and a visible `.tool-call`
  * line (own icon + accent color, distinct from the brand-ink Thinking
  * block) is appended above the answer, one per call, in order.
  * Append-only like thinking: frames are tolerated in any interleaving
@@ -111,6 +112,14 @@ const banner = document.querySelector("#kb-banner");
 const bannerText = document.querySelector("#kb-banner-text");
 const versionEl = document.querySelector("#app-version");
 
+/* Phase 39: the display name resolves from one place — window.BOR_BRAND
+ * (the classic assets/brand.js sets it at parse time; its /api/config
+ * fetch refreshes it). Read LAZILY (a function, not a const string):
+ * a label set after the fetch lands carries the configured name; the
+ * literal below is only the no-config fallback — with the default name
+ * every label renders the pre-phase-39 bytes. */
+const brand = () => window.BOR_BRAND || "Brain of Reese";
+
 /* ---------- loading-feedback contract (PLAN §7.4) ----------
  * Client-side guard: a pre-token stream that produces no delta within
  * TURN_TIMEOUT_MS is treated as hung → error state + banner. It is
@@ -126,14 +135,20 @@ const UI_STATE = Object.freeze({
   error: "error",
 });
 
+/* The #send-status live-region text per UI state (PLAN §7.4). The
+ * values are builders (phase 39): the brand entries resolve brand() at
+ * call time, never at module evaluation, so a label set after the
+ * /api/config fetch lands carries the configured name. */
 const SEND_STATUS = Object.freeze({
-  [UI_STATE.idle]: "",
-  [UI_STATE.thinking]: "Brain of Reese is thinking",
-  [UI_STATE.streaming]: "Brain of Reese is answering",
-  [UI_STATE.error]: "The last question failed — try again",
+  [UI_STATE.idle]: () => "",
+  [UI_STATE.thinking]: () => `${brand()} is thinking`,
+  [UI_STATE.streaming]: () => `${brand()} is answering`,
+  [UI_STATE.error]: () => "The last question failed — try again",
 });
 
-const TYPING_LABEL = "Brain of Reese is thinking";
+/* The typing indicator's accessible label (the 10s elapsed-seconds
+ * hint updates it from this base) — built at call time (phase 39). */
+const TYPING_LABEL = () => `${brand()} is thinking`;
 const ERROR_HINT = "Try again — if this persists, check the LLM is reachable.";
 /* A turn with no answer content (an empty stream, or reasoning that
    exhausted max_tokens — phase 17) still renders a bubble, and this exact
@@ -350,7 +365,7 @@ function addTyping() {
   wrap.innerHTML = `
     <span class="avatar" aria-hidden="true">${BRAIN_AVATAR}</span>
     <div class="msg-body">
-      <div class="bubble typing" role="status" aria-label="${TYPING_LABEL}">
+      <div class="bubble typing" role="status" aria-label="${TYPING_LABEL()}">
         <span></span><span></span><span></span>
       </div>
     </div>`;
@@ -528,7 +543,7 @@ function startThinkingClock() {
     if (secs < 10) return; // hint only after 10s of pre-token silence
     const bubble = document.querySelector("#typing-indicator .bubble");
     if (bubble) {
-      bubble.setAttribute("aria-label", `Brain of Reese is still thinking (${secs}s)`);
+      bubble.setAttribute("aria-label", `${brand()} is still thinking (${secs}s)`);
     }
   }, 1000);
 }
@@ -556,7 +571,7 @@ export function setUiState(state, errorDetail = "") {
   sendBtn.disabled = inFlight;
   sendBtn.querySelector(".spinner").hidden = !inFlight;
   sendLabel.textContent = inFlight ? "Thinking…" : "Send";
-  sendStatus.textContent = SEND_STATUS[state] ?? "";
+  sendStatus.textContent = SEND_STATUS[state]?.() ?? "";
 
   if (state === UI_STATE.thinking) {
     addTyping();
@@ -963,8 +978,8 @@ async function handleSend(e) {
         if (!wrap) wrap = addMessage("brain", "");
         const toolStatus =
           name === "read_document" && argument
-            ? `Brain of Reese is reading ${argument}`
-            : "Brain of Reese is listing documents";
+            ? `${brand()} is reading ${argument}`
+            : `${brand()} is listing documents`;
         if (uiState === UI_STATE.thinking) {
           sendLabel.textContent = "Calling tool…";
           sendStatus.textContent = toolStatus;