feat: add i18n support with zh-CN locale

[LimFang]

Summary

Adds first-class i18n support to goal mode, starting with Simplified Chinese (zh-CN), while preserving English as the default behavior.

Related issue

Closes #52

Changes

• add a locale option with "en" as the default
• support "zh-CN" for Simplified Chinese and "auto" for locale detection from LC_ALL, LANG, then the OS/runtime locale
• add shared English and zh-CN message catalogs without introducing a runtime dependency
• localize /goal, /pause_goal, and /resume_goal prompt templates and command descriptions
• localize V1/V2 goal tool descriptions and user-facing goal notices/reports
• localize continuation, safety-limit wrap-up, system reminder, and compaction prompts
• localize V1/V2 TUI sidebar, dialogs, toasts, and command-palette text
• ship src/i18n.ts with the package because the TUI source imports it
• document the locale option and OpenCode 1 TUI configuration in the README
• add regression coverage for locale resolution, server surfaces, continuation/wrap-up prompts, and V2 TUI labels

Verification

Local verification was performed with Bun 1.4.2:

• bun run lint passes
• bun run typecheck passes
• bun run build passes
• dist/server.js was regenerated and committed
• the i18n-specific regression tests pass
• the full test suite reaches 277/278 passing locally

The remaining failures are in existing timing-sensitive watchdog/restart tests. Both are reproducible on the unmodified upstream main under the same environment:

• V2 watchdog no-response counts a failure on idle even with auto_continue false: 1/10 isolated runs passed
• restart resolves a persisted started pending attempt at the next idle: 37/50 isolated runs passed

The upstream GitHub Actions workflow is still awaiting maintainer approval because this PR originates from a fork.

Checklist

• bun run test passes

  • Local full-suite result: 277/278 tests passed.

  • The remaining failures are in existing timing-sensitive watchdog/restart tests and are reproducible on the unmodified upstream main under the same Bun 1.4.2 environment:

    • V2 watchdog no-response counts a failure on idle even with auto_continue false: 1/10 isolated runs passed on upstream main
    • restart resolves a persisted started pending attempt at the next idle: 37/50 isolated runs passed on upstream main

• bun run lint passes

• bun run typecheck passes

• bun run build passes and dist/server.js is committed

• README/docs updated if behavior or options changed

[danyel117]

Thanks for the thorough i18n work. The full local gate passes at efebf958 (lint, typecheck, 278 tests, build, and pack dry-run), but I found three medium localization gaps that need to be addressed before merge:

1. src/server.ts:1303 and src/server.ts:1992 call continuationPrompt(current) without the configured locale. Both V1 and V2 watchdog rescues therefore fall back to English under locale: "zh-CN". Please pass locale in both paths and add watchdog-level regression tests (not only prompt-builder tests), then rebuild dist/server.js.
2. src/tui.ts:406, src/tui.ts:438, and src/tui.ts:609 translate the Status label but render the raw protocol value (paused, budgetLimited, etc.); plugin-owned stopReason values are also emitted in English. Please add locale-aware presentation mappings while preserving protocol values internally. The current zh-CN test expecting 状态: paused should assert the translated value instead. User/authored free text should remain unchanged.
3. src/prompts.ts:139-140 embeds raw lifecycle status and plugin-owned English stop reasons in the zh-CN safety-limit wrap-up prompt. Please format those known values for presentation before interpolation.

[LimFang]

Thanks for the detailed review. All three localization gaps have now been addressed.

Both V1 and V2 watchdog rescue paths now correctly propagate the configured locale, with zh-CN regression coverage added at the watchdog level.
TUI lifecycle statuses and plugin-owned stop reasons are now localized for display, while keeping protocol values unchanged internally. User-provided text is intentionally left untouched.
The zh-CN safety-limit wrap-up prompt now localizes known lifecycle statuses and stop reasons.
Updated the V2 zh-CN TUI expectation from 状态: paused to 状态: 已暂停.
Rebuilt dist/server.js.

Validation results:

bun run lint ✅
bun run typecheck ✅
bun run build ✅
npm pack --dry-run ✅
Full test suite: 279/281 passed on Bun 1.4.2.

The two remaining failures are the previously documented timing-sensitive watchdog/restart tests. They are reproducible on the unmodified upstream main branch under the same environment. All newly added and modified i18n regression tests pass.

[danyel117]

Re-reviewed at 21158c0. The localization gaps are resolved, the Chinese prompts preserve the English safety semantics, and V1/V2 command arguments are structurally escaped to prevent delimiter breakout while keeping legitimate objectives actionable. Local gate: lint, typecheck, 291 tests, build, and pack dry-run all pass. No remaining high/medium review findings.