fix: restore Playwright MCP package default

[numnx]

What changed

• restore the built-in Playwright MCP stdio configuration to npx with @playwright/mcp@latest as its argument
• migrate already-saved untouched playwright-mcp entries with no arguments to the package-backed configuration during settings resolution
• update provider serialization and migration regression tests
• document the default and compatibility migration in canonical and published MCP docs

Why

A managed-runtime change replaced the standard Playwright MCP package invocation with a presumed playwright-mcp executable. That executable is not guaranteed to exist in chat-agent runtimes, so the linked Playwright server could not start and its browser tools were unavailable.

This restores the upstream-supported client configuration and repairs existing seeded settings without overwriting other user-defined Playwright commands or arguments.

Validation

• pnpm run ci — passed
  • quality guardrails
  • dependency audit (no known vulnerabilities)
  • strict typecheck/lint
  • backend tests and coverage: 5,105 passed, 7 skipped; 83.52% lines
  • dashboard tests: 1,996 passed, 2 skipped
  • production build
• pnpm run check:docs-web — passed
• live runtime /health — UP after restart
• live system settings expose command: npx and args: ["@playwright/mcp@latest"]
• npx @playwright/mcp@latest --help — package resolved and CLI started successfully

Risk and rollback

Risk is limited to the built-in Playwright MCP launch command. The migration only recognizes the legacy no-argument playwright-mcp shape associated by stable id or name; other custom commands remain unchanged.

Rollback by reverting this commit. Existing settings would then resolve to the prior baked-executable command again.