chore(ci): remove upstream workflows not needed for internal fork

[terisuke]

Problem

The fork carries 27 GitHub Actions workflow files from upstream that are not needed.

Verified facts (via git diff --stat and ls .github/workflows/)

• 27 workflow files deleted, 1 modified (test.yml), 2715 lines removed
• 5 workflows remain: generate.yml, pr-management.yml, pr-standards.yml, test.yml, typecheck.yml
• test.yml: Windows matrix entries removed (0 windows references after change)

Deleted workflows

beta, close-issues, close-stale-prs, compliance-close, containers, daily-issues-recap, daily-pr-recap, deploy, docs-locale-sync, docs-update, duplicate-issues, nix-eval, nix-hashes, notify-discord, opencode, publish-github-action, publish-vscode, publish, release-github-action, review, stats, storybook, sync-zed-extension, triage, vouch-check-issue, vouch-check-pr, vouch-manage-by-issue

[terisuke]

受入基準全項目確認済み。

受入基準1: 27 upstream workflowファイル削除

• PR chore(ci): prune upstream workflows and add upstream sync #61 (merged 2026-04-05T06:54:14Z) で29ファイル変更、27 workflow削除
• 残存ワークフロー: .github/workflows/{generate,pr-management,pr-standards,test,typecheck,upstream-sync}.yml (6ファイル)

受入基準2: test.yml簡素化 (Windows matrix削除)

• .github/workflows/test.yml:4-8 — push: branches: [dev] + pull_request_target に変更
• Windows matrix entries: 0 (commit 02564b0 で削除済み)

受入基準3: typecheck.yml fork runner互換

• .github/workflows/typecheck.yml:6 — pull_request_target に変更 (PR fix(ci): use pull_request_target for fork runner compatibility #64, merged 2026-04-05T08:07:16Z)

受入基準4: upstream-sync追加

• .github/workflows/upstream-sync.yml:1-10 — NEW, weekly Monday 9am UTC cron + workflow_dispatch

PRs:

• PR chore(ci): prune upstream workflows and add upstream sync #61: chore(ci): prune upstream workflows and add upstream sync (MERGED)
• PR fix(ci): use pull_request_target for fork runner compatibility #64: fix(ci): use pull_request_target for fork runner compatibility (MERGED)

CI結果:

• pr-standards: completed/success
• Copilot code review: completed/success