Add ClawMaster release notifications

[webup]

What

Adds in-app ClawMaster release detection and notification UI. The app now checks GitHub Releases first, falls back to npm metadata when GitHub is slow or unavailable, shows a dismissible release banner, and adds a Settings section with rendered release notes, installer selection, and upgrade links.

Why

Users need a visible way to discover new ClawMaster app releases and a clear path to upgrade without confusing those app releases with OpenClaw CLI updates.

How

• Inject the current ClawMaster package version into the web app at build time.
• Add a shared release adapter that compares versions, loads GitHub release details, and falls back to npm through the backend or Tauri command path.
• Extend npm proxy handling so npm view uses the configured mirror as well as installs.
• Add a Settings release section with safe Markdown rendering for release notes and platform-specific installer selection.
• Update the layout banner to point at the new release section and persist dismissals per release version.

Issue

Closes #129

Screenshots

Verified in the in-app browser at http://127.0.0.1:16224/settings?demo=1; the ClawMaster release section rendered Markdown headings and fenced command blocks without showing raw Markdown syntax.

Testing

• npx vitest run src/shared/adapters/__tests__/clawmasterReleases.test.ts src/app/__tests__/Layout.test.tsx src/modules/settings/__tests__/UpdateSection.test.tsx
• npx vitest run src/modules/settings/__tests__/UpdateSection.test.tsx
• npx vitest run src/modules/settings/__tests__/CapabilitiesSection.test.tsx
• npm --prefix packages/backend test -- src/npmProxy.test.ts
• npm run build
• npm run build:backend
• cargo check