feat: add benchmark seed provisioning (task 0025)

Add the deterministic, idempotent seed that brings a freshly provisioned
throwaway repository to a known ground truth before a trial runs, scripted
over the live Gitea API.

- bench/seed-plan.ts: the pure ground truth (fixed labels, an issue spread
  across the discriminating dimensions, and labelled/reviewed/real-branch
  pull requests) plus groundTruth(user), realizing it into a RepoState.
- bench/seed.ts: idempotent seeding reconciled by natural key, reusing
  gitea-axi's own tea-login credential discovery (no new secret handling).
- A live smoke tier (test:bench:smoke) validating the seed end-to-end and
  skipping cleanly when no host is configured, kept out of the deterministic
  bench tier.

Export selectLogin from src/context.ts so the bench reuses the exact
credential-selection path.

vitest.bench-smoke.config.ts

@@ -0,0 +1,17 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    // The seed smoke tier: a single live end-to-end validation that provisioning
+    // and seeding a throwaway repository really brings it to the ground truth,
+    // and that re-seeding is idempotent. Like the e2e tier, it targets a live
+    // host — here the maintainer's own, discovered through gitea-axi's tea-login
+    // credential path — and skips cleanly when none is configured
+    // (GITEA_AXI_BENCH_LOGIN unset), which must count as a pass, not "no tests
+    // found". It is deliberately kept out of the deterministic bench tier.
+    include: ["bench/**/*.smoke.test.ts"],
+    testTimeout: 60_000,
+    hookTimeout: 180_000,
+    passWithNoTests: true,
+  },
+});