fix(tun): drive tun2socks through its YAML config

[loss-and-quick]

Summary

The v2.6.0 → v2.7.0 tun2socks bump (shipped in v0.4.3) broke the tun2socks TUN engine on desktop and Android: upstream switched CLI parsing from stdlib flag to spf13/pflag, which rejects the single-dash long flags spawn_tun2socks passed — -mtu parses as shorthand -m and the binary exits with unknown shorthand flag: 'm' in -mtu.

Instead of just re-dashing the flags, tun2socks is now driven through its YAML config file (--config, supported by both v2.6.0 and v2.7.0), mirroring the hev path:

• new kasumi_core::tun2socks_config::build_tun2socks_config renders the config (device, proxy, mtu, loglevel, udp-timeout, tcp-send/receive-buffer-size, optional fwmark), consuming the same TunOptions knobs that already reach hev — previously only mtu and fwmark made it to tun2socks;
• spawn_tun2socks writes the config and launches <bin> --config <cfg>;
• tun2socks gets its own config path instead of borrowing hev's: tun2socks.yml in run_dir on desktop (Linux + Windows), tun2socks.yml/tun2socks2.yml consts on Android (the 2 variant for the force-proxy tun).

Wire-format note: upstream's udp-timeout is a Go time.Duration; its YAML parser accepts a duration string (60000ms) but rejects a bare integer, so the generator emits the string form.

frontend/src/generated/bindings.ts is codegen output of the updated AdvancedSettings doc comments.

Affected layer

• frontend/ — React Web UI
• crates/ · src-tauri/ — Rust core / backend / Tauri desktop
• module/ — Android installable zip (thin launcher over the Rust daemon)
• scripts/ — build / release helpers
• CI / .github/
• Docs only

Verification

Rust (crates/ · src-tauri/):

• cargo fmt --all --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace — one failure: net::tests::tcp_ping_fails_on_unreachable_host, the known local-sandbox flake (TEST-NET-1 connect is intercepted by the dev environment; net.rs untouched)
• Codegen drift: cargo run -p kasumi-desktop --bin codegen leaves git clean

Web UI (frontend/):

• bun run check — only generated bindings.ts changed, which Biome ignores by config
• bun run test — no such script in package.json
• bun run build — tsc -b + vite build succeed
• bun run check:i18n — no user-visible strings changed

Additionally, against the real release binaries (both the staged v2.6.0 and the downloaded v2.7.0):

• old single-dash argv reproduces the failure on v2.7.0;
• the generated YAML parses cleanly on both versions and reaches TUN device creation (fails there only on missing privileges, as expected unprivileged).

Checklist

• Title is a scoped Conventional Commit; commits are logically split
• No build artifacts committed (module/bin/<abi>/, geoip/geosite, built module/webroot/, src-tauri/gen/ — all gitignored on purpose)
• Generated frontend/src/generated/ was regenerated from Rust, not hand-edited
• If user-visible strings changed: i18n/en.ts and every locale file updated (no partial translations)
• Renames touching the project id were grepped in all case forms (kasumi-proxy, Kasumi Proxy, camelCase)

Notes for reviewers

Not exercised: live TUN bring-up end-to-end (needs the privileged helper); the config content itself was validated against both real binaries as above. TunOptions knobs without a tun2socks equivalent (connect_timeout_ms, tcp_rw_timeout_ms, udp_recv_buffer_size) are intentionally not emitted.