Add community Rust client (rust/)

[enrell]

Community Rust client

Adds a Rust wrapper under rust/, following the same monorepo conventions as the first-party .NET client (dotnet/, PR #385): self-contained crate + CLI + examples + unit tests, built on playwright-rs.

This is a faithful port of the open-source wrapper surface (not the Chromium binary). Behavior targets parity with Python / JS / .NET for launch flags, download verification, Pro routing, proxy/GeoIP/WebRTC, and humanized input.

Conventions followed

• Layout: rust/ at the repo root, alongside cloakbrowser/ (Python), js/, and dotnet/. Workspace with cloakbrowser (lib) + cloakbrowser-cli (bin) + examples.
• Versioning: wrapper version 0.4.10, matching the current monorepo release.
• Docs: rust/README.md is the client guide (feature matrix, API, env vars, Python→Rust mapping). Root README gets a short Install blurb + Latest bullet; CHANGELOG.md has an [Unreleased] entry.
• CI: new rust job in .github/workflows/ci.yml runs cargo test -p cloakbrowser --lib (browser-free unit tests).

What's ported

Area	Notes
Binary lifecycle	Download / cache / auto-update; pinned Ed25519 on SHA256SUMS.sig + SHA-256; version binding (anti-downgrade); zip-slip guard
Launch	Stealth args, ignore automation defaults, proxy HTTP/HTTPS + SOCKS5 (inline creds gated by binary version), GeoIP timezone/locale, WebRTC =auto, extensions, license env injection
Pro	license_key / CLOAKBROWSER_LICENSE_KEY / ~/.cloakbrowser/license.key; 24h cache; Pro path never silently falls back to free on verification failure
Persistent context	launch_persistent_context + viewport auto/Size/NoViewport; Linux Widevine hint seeding
Humanize	Explicit HumanPage (Bezier mouse, typing + CDP shift symbols, scroll bursts). Rust cannot monkey-patch Playwright's sealed Page — same design pressure as .NET's decorator layer
CLI	install / info / update / clear-cache

Not in this PR (intentionally)

• Transparent Playwright interface wrapping for every Page method (would be a large generator like the .NET Roslyn source generator). Callers use new_human_page() / HumanPage for humanized actions and page() for the raw Playwright surface.
• crates.io publish / release automation (happy for maintainers to own packaging).
• Full actionability matrix / iframe humanize parity with the latest Python frame-routing work.

Tests

cd rust
cargo test -p cloakbrowser --lib   # 34 passed
cargo clippy -p cloakbrowser --lib -- -D warnings

Coverage includes version pins, checksum/manifest parsing, zip-slip, stealth arg composition, proxy SOCKS/HTTP resolution, viewport defaults, Bézier math, keyboard nearby-key map, Widevine no-ops, and license env injection.

Build & try locally

cd rust
cargo run -p cloakbrowser-cli -- install
cargo run -p cloakbrowser-cli -- info --quick
cargo run --example basic -p cloakbrowser
cargo run --example humanize -p cloakbrowser
cargo run --example persistent_context -p cloakbrowser

Happy to adjust naming, CI pins, docs wording, or drop root-README/CHANGELOG touches if you'd rather land those in a follow-up (the .NET PR originally left those to maintainers).