feat(web): add complete product documentation - #144

Summary

• add source-backed install, MCP, command reference, security, platform comparison, and changelog routes
• derive product/protocol versions, release history, MCP configuration, security boundaries, install commands, and all 52 CLI forms from checked-in canonical sources
• add shared documentation navigation, responsive tables and release history, route-level metadata, robots.txt, sitemap.xml, and a no-index 404 page
• extend web lint to reject missing routes, stale package versions, divergent MCP configs, incomplete command/security/install content, or truncated release history
• replace the repository-specific remote MCP hostname with a portable example

Security and provenance

• repository reads use fixed, bounded, regular-file paths and fail the build on malformed source documents
• rendered source content remains React-escaped text; no raw HTML, runtime fetch endpoint, or client-side filesystem access is introduced
• browser-control guidance preserves stdio/private-socket boundaries and explicitly documents destructive MCP operations

Validation

• pnpm test (45/45 protocol/security tests and MCP integration)
• pnpm test:runtime
• pnpm test:npm
• pnpm --dir apps/web lint
• pnpm --dir apps/web build
• pnpm test:e2e:linux
• ./apps/headless/build.sh
• npm package dry run, shell syntax checks, QA evidence checksums, and git diff --check
• Prettier 3.6.2 check for every changed file
• production browser QA for all six routes, custom 404, crawler outputs, metadata titles, console errors, and visual layout

Closes #49