feat(web): topic chat UI over /api/v1/* (v0.2.0)

New dashboard route at /dashboard/meshes/[id]/topics/[name] gives signed-in
users a thin chat client over the v0.2.0 REST surface. The mesh detail page
now lists topics with one-click links into the chat. Backend layout:

- packages/api/src/modules/mesh/api-key-auth.ts — exports
  createDashboardApiKey() that mints a 24h read+send key scoped to a single
  topic for the caller's member id. The page server component calls this on
  every render and embeds the secret in the props of the client component;
  the secret never touches sessionStorage so a tab close = key effectively
  abandoned (the row remains until expiresAt).
- apps/web/.../topics/[name]/page.tsx — server component, NextAuth gate,
  resolves the user's meshMember.id, mints the key, renders the shell.
- apps/web/src/modules/mesh/topic-chat-panel.tsx — client component, polls
  GET /v1/topics/:name/messages every 5s, sends via POST /v1/messages.
  Encoding wraps base64(plaintext) into the ciphertext field — matches the
  current broker contract until per-topic HKDF lands in v0.3.0.

The mesh detail page gains a Topics section with empty-state copy that
points users at the CLI verb (claudemesh topic create) for now; topic
creation from the web UI is a follow-up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/api/package.json

@@ -7,7 +7,8 @@
     ".": "./src/index.ts",
     "./env": "./src/env.ts",
     "./utils": "./src/utils/index.ts",
-    "./schema": "./src/schema/index.ts"
+    "./schema": "./src/schema/index.ts",
+    "./modules/mesh/api-key-auth": "./src/modules/mesh/api-key-auth.ts"
   },
   "scripts": {
     "clean": "git clean -xdf .cache .turbo dist node_modules",