feat: cancel export subtitle translations

[ringoshiina]

Summary

• Add an export-scoped cancellation group for translated subtitle SRT export and cancel that group when the downloader is disposed.
• Teach the subtitle translation queues to reject pending and executing work by cancellation group, including a short-lived late-enqueue guard for requests that arrive after cancellation.
• Keep ungrouped subtitle/page translation behavior unchanged while separating cancellation groups from the existing request de-dupe/cache path.

Scope

This PR intentionally does not:

• abort provider HTTP requests that are already in flight;
• add a user-facing cancel button;
• add background or resumable export behavior.

Validation

• pnpm exec vitest run src/entrypoints/background/__tests__/translation-queues.test.ts
• pnpm exec vitest run src/entrypoints/subtitles.content/__tests__/translated-subtitles-downloader.test.ts src/utils/subtitles/processor/__tests__/translator.test.ts
• pnpm exec vitest run src/utils/request/__tests__/request-queue.test.ts src/utils/request/__tests__/batch-queue.test.ts
• pnpm exec tsc --noEmit --pretty false
• pnpm exec eslint src/entrypoints/background/translation-queues.ts src/entrypoints/background/__tests__/translation-queues.test.ts src/entrypoints/subtitles.content/translated-subtitles-downloader.ts src/entrypoints/subtitles.content/__tests__/translated-subtitles-downloader.test.ts src/utils/message.ts src/utils/request/request-queue.ts src/utils/request/batch-queue.ts src/utils/subtitles/processor/translator.ts src/utils/subtitles/processor/__tests__/translator.test.ts
• git diff --check
• pre-push hook: @read-frog/extension:lint, @read-frog/extension:type-check, @read-frog/extension:test (159 test files, 1341 tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: b4fe70c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@read-frog/extension	Patch

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[github-actions]

Contributor trust score

32/100 — Moderate

This score estimates contributor familiarity with mengxi-ream/read-frog using public GitHub signals. It is advisory only and does not block merges automatically.

Outcome

• PR: feat: cancel export subtitle translations #1701 — feat: cancel export subtitle translations
• Author: @ringoshiina
• Trust label: contrib-trust:moderate
• Maintainer review: not required
• Override label: add trust-check:skip to stop future trust automation updates

Score breakdown

Dimension	Score	Signals
Repo familiarity	14/35	commits in repo, merged PRs, reviews
Community standing	6/25	account age, followers, repo role
OSS influence	3/20	stars on owned non-fork repositories
PR track record	9/20	merge rate across resolved PRs in this repo

Signals used

• Repo commits: 3 (author commits reachable from the repository default branch)
• Repo PR history: merged 3, open 1, closed-unmerged 2
• Repo reviews: 0
• PR changed lines: 705 (+664 / -41)
• Repo permission: read
• Followers: 1
• Account age: 95 months
• Owned non-fork repos considered: max 1, total 1 (ringoshiina/learn-quiz-skill (1), ringoshiina/shadowrocket-backcn-rules (0), ringoshiina/QuickShot_v2 (0))

Policy

• Low-score review threshold: < 30
• Auto-close: score < 20 and changed lines > 1000
• Policy version: v1.1

Updated automatically when the PR changes or when a maintainer reruns the workflow.

[mengxi-ream]

We have been busy with other features recently. This PR appears to modify the capabilities of our core underlying queue, which is quite risky, and we currently don't have time for a detailed review. I will mark this PR as "on hold" for now. When we have more time in the future, we will come back to review it. Sorry about that.