docs(eval): Phase 3 contributor docs + CI workflow for eval/ tests

Ships the contributor-onboarding surface promised in the plan. With this
commit, external researchers have a self-serve path from clone to PR in
under 5 minutes.

Added:
  eval/README.md                                — 5-minute quickstart,
                                                  directory map, methodology
                                                  one-pager, adapter scorecard
  eval/CONTRIBUTING.md                          — three contributor paths:
                                                    1. Write Tier 5.5 queries
                                                    2. Submit an external adapter
                                                    3. Reproduce a scorecard
  eval/RUNBOOK.md                               — operational troubleshooting:
                                                  generation failures, runner
                                                  failures, query validation,
                                                  world.html rendering, CI
  eval/CREDITS.md                               — contributor attribution
                                                  (synthetic-outsider-v1 labeled
                                                  as placeholder; real submissions
                                                  land here)
  .github/PULL_REQUEST_TEMPLATE/tier5-queries.md — structured PR template
                                                  for Tier 5.5 submissions
  .github/workflows/eval-tests.yml              — CI: validates queries,
                                                  runs all eval unit tests,
                                                  renders world.html on every PR
                                                  touching eval/** or
                                                  src/core/link-extraction.ts

CI scope (intentionally narrow):
  - Triggers on paths: eval/**, src/core/link-extraction.ts, src/core/search/**
  - Runs: bun run eval:query:validate (80 queries), test:eval (57 tests),
          eval:world:render (smoke-test the HTML renderer)
  - Pinned actions by commit SHA (matches existing .github/workflows/test.yml)
  - Zero API calls — all Opus/OpenAI paths stubbed or skipped in unit tests
  - Fast: ~30s total wall clock

Contributor TTHW (clone → first merged PR):
  - Path 1 (Tier 5.5 queries): ~5 min
  - Path 2 (external adapter): ~30 min for a simple adapter
  - Path 3 (reproduce scorecard): ~15 min wall clock (N=5 run)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/PULL_REQUEST_TEMPLATE/tier5-queries.md

@@ -0,0 +1,39 @@
+<!--
+Tier 5.5 Externally-Authored Query Submission template
+See eval/CONTRIBUTING.md for the full workflow.
+-->
+
+## Summary
+
+Submitting **N** Tier 5.5 queries for BrainBench.
+
+- Author handle: `@your-handle`
+- File location: `eval/external-authors/your-handle/queries.json`
+- Queries authored fresh (not copy-pasted from a model output)
+- Slugs verified against `eval/data/world-v1/` (via `bun run eval:world:view`)
+
+## Checklist
+
+- [ ] `bun run eval:query:validate eval/external-authors/your-handle/queries.json` passes
+- [ ] At least 20 queries
+- [ ] Each query has either `gold.relevant` (with real slugs) or `gold.expected_abstention: true`
+- [ ] Temporal queries have `as_of_date` set (`corpus-end` | `per-source` | ISO-8601)
+- [ ] Phrasing is varied (not all the same template)
+- [ ] `author` field matches my handle
+
+## Phrasing variety (optional self-audit)
+
+Tick the styles represented in your batch:
+
+- [ ] Full sentence questions
+- [ ] Fragment-style ("crypto founder Goldman Sachs background")
+- [ ] Comparison ("X vs Y")
+- [ ] Follow-up ("And who else...")
+- [ ] Imperative ("Pull up Alice Davis")
+- [ ] Trait-based ("the demanding engineering leader")
+- [ ] Abstention bait (answer is "not in corpus")
+
+## Notes to reviewer
+
+Anything worth flagging — ambiguous cases, corpus gaps you found, specific
+phrasings you were uncertain about.

.github/workflows/eval-tests.yml

@@ -0,0 +1,40 @@
+name: Eval tests
+
+on:
+  push:
+    branches: [master]
+    paths:
+      - 'eval/**'
+      - 'src/core/link-extraction.ts'
+      - 'src/core/search/**'
+  pull_request:
+    branches: [master]
+    paths:
+      - 'eval/**'
+      - 'src/core/link-extraction.ts'
+      - 'src/core/search/**'
+
+permissions:
+  contents: read
+
+jobs:
+  eval-tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4
+      - uses: oven-sh/setup-bun@0c5077e51419868618aeaa5fe8019c62421857d6  # v2
+        with:
+          bun-version: latest
+      - run: bun install
+
+      # Validate the built-in Tier 5 + 5.5 query set.
+      - name: Validate built-in queries
+        run: bun run eval:query:validate
+
+      # Pure-function unit tests — zero API calls, fast.
+      - name: Run eval unit tests
+        run: bun run test:eval
+
+      # Smoke-test the world.html renderer against the committed corpus.
+      - name: Render world.html
+        run: bun run eval:world:render