feat(i18n): add Turkish (tr-TR) locale support

[macbyclp]

Summary

Adds Turkish (tr-TR) as a full UI language option.

• New Language::Turkish variant across rust/src/settings/types.rs and rust/src/locale.rs, wired to a new tr-TR Fluent bundle.
• New rust/src/locale/tr-TR.ftl with all 758 locale keys translated.
• Bridge/TS types and the GeneralTab language picker updated to expose turkish as a selectable option.
• New README.tr-TR.md (full translation) and a language-switcher link added to README.md and the other localized READMEs.
• Tests added/updated for the new locale in locale_cmd.rs, rust/src/locale/tests.rs, rust/src/settings/tests.rs, and GeneralTab.test.tsx / bridge.test.ts.

Testing

Ran from repo root (MSVC toolchain; the default GNU toolchain in my environment is missing dlltool.exe):

node apps/desktop-tauri/scripts/check-locale-drift.mjs
cargo +stable-x86_64-pc-windows-msvc test --manifest-path rust\Cargo.toml locale
cargo +stable-x86_64-pc-windows-msvc test --manifest-path apps\desktop-tauri\src-tauri\Cargo.toml locale
cargo +stable-x86_64-pc-windows-msvc fmt --all -- --check
pnpm --dir apps\desktop-tauri test

Results:

• check-locale-drift: OK, 758 keys match between Rust and TS
• rust\Cargo.toml locale tests: 16 passed
• tauri crate locale tests: 9 passed (includes new locale_strings_roundtrip_turkish)
• cargo fmt --check: clean
• pnpm test: 258 passed across 42 files

No UI/tray visual behavior changed beyond adding one more entry to the existing language <select>, so no CUA Driver capture was produced for this PR; happy to add one if maintainers want a screenshot of the new option in the Settings > General language picker.

[Finesssee]

Thanks for the PR, I will review this ASAP.