fix(test): stop rebuilding env/keys per iteration in repo-name validation tests - #6880

Summary

• test/unit/github-labels.test.ts's "rejects invalid repository names before making GitHub calls" and test/unit/github-pr-actions.test.ts's "validates the repo name before any GitHub call" each called createTestEnv() up to 9 times, and generated a fresh RSA-2048 key (generateRsaPrivateKeyPem(), real synchronous CPU work) up to 4 times -- once per malformed-name case in a loop.
• ensurePullRequestLabel/closePullRequest reject on parseRepoFullName()/splitRepo() before ever touching env (src/github/labels.ts, src/github/pr-actions.ts), so none of that setup was needed more than once per env-shape (plain vs. keyed).
• These were reported as timing out alongside three already-merged sibling fixes for the same general class of problem (real subprocess/DB setup work exceeding vitest's timeout under heavy concurrent load): test/unit/ai-summaries.test.ts (fix(test): stop ai-summaries forbidden-word sweep timing out under load #6874), test/unit/agent-sdk-driver.test.ts (fix(test): reduce and widen the agent-sdk-driver real-git test timeout #6871), and the #5132 miner clone/worktree suite (fix(test): widen timeouts on real-git miner clone/worktree tests #6869).
• This pair didn't reproduce under realistic load, though: 3x isolated runs and 3x runs under simulated CPU contention (16 processes oversubscribing a 12-core machine) all passed cleanly, with neither target test ever appearing among the slowest tests in its file. The original failure was traced to two full ~18k-test suites running concurrently on one machine (two worktrees' npm run test:ci backgrounded at the same time) -- a self-inflicted, unrealistic doubling of load, not a normal-load risk.
• Fixing the confirmed redundant setup anyway since it's the exact same safe, zero-behavior-change pattern already proven on the three sibling PRs, and it measurably speeds up the suite regardless: ~20% faster on both files together under sustained load (44.7s/45.4s/40.9s fixed vs. 56.0s/56.4s/54.8s baseline, 3 runs each, same continued CPU-contention conditions). No timeout was widened -- there was nothing to widen; this is purely eliminating unnecessary setup.

Scope

• The PR title follows type(scope): short summary Conventional Commit format.
• This PR is focused and does not mix unrelated backend, UI, MCP, docs, dependency, and deploy changes.
• This follows CONTRIBUTING.md and does not reintroduce GitHub Pages, VitePress, site/, or CNAME.
• I linked a currently open issue this PR resolves -- not applicable; this is a maintainer-authored test-reliability fix, not a contributor PR under the linked-issue policy.

Validation

• git diff --check
• npm run actionlint
• npm run typecheck
• npm run test:coverage locally -- test-only change to test/**, which Codecov does not measure, so there is no patch-coverage obligation.
• npm run test:workers
• npm run build:mcp
• npm run test:mcp-pack
• npm run ui:openapi:check
• npm run ui:lint
• npm run ui:typecheck
• npm run ui:build
• npm audit --audit-level=moderate
• New or changed behavior has unit/integration tests for new branches, fallback paths, and sanitizer boundaries -- not applicable; no production code changed, and both files' full 58 tests still pass unchanged.

Additional validation beyond the standard checklist: both target tests run 3x in isolation and 3x under simulated heavy CPU contention with zero failures (see timing data in Summary). A full local npm run test:ci run (single suite, not concurrent with anything else) shows both github-labels.test.ts and github-pr-actions.test.ts fully clean.

Safety

• No secrets, wallet details, hotkeys, coldkeys, user PATs, private keys, raw trust scores, private rankings, or private maintainer evidence are exposed.
• Public GitHub text stays sanitized, low-noise, and does not imply compensation guarantees or optimization tactics. (Not applicable -- test-only change.)
• Auth, cookie, CORS, GitHub App, Cloudflare, or session changes include negative-path tests. (Not applicable -- no such changes.)
• API/OpenAPI/MCP behavior is updated and tested where needed. (Not applicable -- no such changes.)
• UI changes use live API data or real empty/error/loading states, not production mock/demo fallbacks. (Not applicable -- no UI changes.)
• Visible UI changes include a UI Evidence section below. (Not applicable -- no visible/UI changes.)
• Public docs/changelogs are updated where needed. (Not applicable.)

UI Evidence

Not applicable -- test-only change, no UI/frontend/docs surface touched.

Notes

• Follow-up from the same investigation as fix(test): stop ai-summaries forbidden-word sweep timing out under load #6874, fix(test): reduce and widen the agent-sdk-driver real-git test timeout #6871, and fix(test): widen timeouts on real-git miner clone/worktree tests #6869. A separate, unrelated bug (a stale gittensory-orb string in test/unit/release-selfhost-prerelease.test.ts, left behind by commit 7c5965d8's otherwise-correct rebrand of .github/workflows/release-selfhost.yml) was also surfaced by this PR's npm run test:ci run and is being fixed in its own separate PR.