feat(dogfood-wave1): fix Studio retries, Chat error, LLM gateway, kill snapshot, topbar cleanup

User dogfood found many bugs. This wave addresses:

- nginx.conf: proxy_next_upstream + retries on 502/503/504, explicit
  proxy_ssl_name, 8s connect timeout. The DNS-resolver race that
  caused the Studio 'apply_patch 502' is now eaten by nginx retry.

- src/lib/wizardApi.ts: applyBatch retries 3x on 502/503/504 with
  exponential backoff. Even if nginx misses the retry the client
  takes a second shot.

- src/lib/chatApi.ts: listThreads now THROWS when ensureInbox fails
  instead of silently returning []. Chat scene shows the error +
  retry button instead of an empty 'No conversations' state that
  hides the real failure.

- src/scenes/Chat.tsx: explicit error banner with 'Try again' button.

- src/lib/llmClient.ts: rewritten to call /api/v1/llm/generate
  (real demo gateway, same as dev.flow-master.ai uses). Removed the
  local /internal/canvas-llm/chat sidecar entirely.

- src/scenes/Agent.tsx: removed the LLM-state probe + 'off by
  default' OFF pill. LLM is now part of the assistant unconditionally.

- src/lib/flowCuration.ts: dropped the STARTABLE_FLOW_KEYS allowlist
  gate in curatedPublishedFlows so list_processes now returns every
  published business process, not just pr_to_po_def.

- src/state/store.ts + tests: DataMode is now 'live' only. Removed
  the SNAPSHOT branch; live is the only mode. Renamed the failure
  toast accordingly. Initial scene is 'mission' not 'landing'.

- src/scenes/Login.tsx + test: post-login navigates to 'mission'
  instead of the empty landing splash.

- src/scenes/Settings.tsx + src/components/CommandBar.tsx: removed
  every snapshot/setMode reference. Settings shows 'EA2 · live
  always'. Command palette no longer offers a snapshot switch.

- src/App.tsx: topbar redesign. Removed Settings + Home tabs
  (now in user menu), removed standalone Light/Dark + Console
  buttons (collapsed into user menu), removed the SNAPSHOT/LIVE
  mode pill + topbar refresh. New UserMenu component shows a 2-char
  avatar circle; clicking opens a dropdown with Home / Settings /
  Refresh data / theme toggle / API console toggle. Topbar now has:
  brand · tabs · cmd-k · notification bell · avatar.

- src/index.css: user-menu styles + chat-err styles + dark variants.

30/30 vitest pass. tsc + vite build green.

qa/_live_after_fix.mjs

@@ -0,0 +1,45 @@
+// Real human dogfood — persona chip click should sign in directly.
+import { chromium } from "playwright";
+
+const URL = "https://canvas.flow-master.ai/";
+
+const b = await chromium.launch({ headless: true });
+const ctx = await b.newContext({ viewport: { width: 1440, height: 900 } });
+const p = await ctx.newPage();
+
+const calls = [];
+p.on("response", (r) => {
+  const u = r.url();
+  if (u.includes("/api/")) calls.push({ status: r.status(), url: u.replace("https://canvas.flow-master.ai", "") });
+});
+
+console.log("[1] Visit canvas.flow-master.ai");
+await p.goto(URL, { waitUntil: "domcontentloaded" });
+await p.waitForTimeout(2000);
+
+console.log("[2] Click CEO persona chip");
+await p.locator(".persona-chip", { hasText: /Mariana/ }).click();
+await p.waitForTimeout(4000);
+
+console.log("[3] Check scene + url");
+const onLogin = (await p.locator(".login-page").count()) > 0;
+const onLanding = (await p.locator(".hero-eyebrow").count()) > 0;
+const sceneClass = await p.evaluate(() => document.querySelector("[class*='shell-']")?.className);
+console.log(`  onLogin=${onLogin}  onLanding=${onLanding}  shell=${sceneClass}`);
+
+console.log("[4] Try Mission");
+await p.locator(".tab", { hasText: /Mission/ }).click().catch(() => {});
+await p.waitForTimeout(3000);
+const onMission = (await p.locator(".bp-node-body, .empty").count()) > 0;
+console.log(`  onMission=${onMission}`);
+
+await p.screenshot({ path: "/tmp/canvas-evidence/05-LIVE-after-fix.png", fullPage: false });
+
+console.log("\n=== API CALLS ===");
+const status = {};
+for (const c of calls) status[c.status] = (status[c.status] || 0) + 1;
+console.log("status counts:", JSON.stringify(status));
+console.log("first 10:");
+for (const c of calls.slice(0, 10)) console.log(`  ${c.status} ${c.url.slice(0, 80)}`);
+
+await b.close();