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>

apps/web/src/config/paths.ts

@@ -99,6 +99,9 @@ const pathsConfig = {
         mesh: (id: string) => `${DASHBOARD_PREFIX}/meshes/${id}`,
         invite: (id: string) => `${DASHBOARD_PREFIX}/meshes/${id}/invite`,
         live: (id: string) => `${DASHBOARD_PREFIX}/meshes/${id}/live`,
+        topics: (id: string) => `${DASHBOARD_PREFIX}/meshes/${id}/topics`,
+        topic: (id: string, name: string) =>
+          `${DASHBOARD_PREFIX}/meshes/${id}/topics/${encodeURIComponent(name)}`,
       },
       invites: `${DASHBOARD_PREFIX}/invites`,
       settings: {