feat: add Windows proxy settings and local file links

[lyumy2500]

What changed

• add Windows HTTP/HTTPS proxy configuration, validation, and localized UI
• make local file references in chat clickable and open them in the right-side viewer
• restrict link styling to real files rather than folders, commands, or model identifiers
• prevent Next.js production tracing from recursively scanning the Windows user profile
• move directory enumeration to runtime and avoid periodic home-directory scans

Why

Windows users need an in-app proxy configuration path and reliable local-file navigation. The production build also failed with EPERM when Next.js expanded runtime filesystem reads into a recursive glob over protected compatibility junctions such as Application Data and Cookies.

Impact

• proxy settings can be configured and tested from pi-web
• chat file references are easier to discover and open
• npm run build succeeds on Windows without requiring ownership or permission changes
• locally packed builds can be installed globally and start normally

Validation

• npm run build (isolated production worktree)
• npx tsc --noEmit
• ESLint on changed build and filesystem files
• file-link, file-access, and directory-enumeration regression checks
• npm pack --json
• installed the generated tarball globally as @agegr/pi-web@0.8.6
• global service smoke test: homepage, sessions API, drive picker, and project directory browse returned HTTP 200