[Fix] Green CI: skip signal-health benchmark when the dogfood DB is absent (regression from ae077b7)

[codenamev]

Problem

main CI (.github/workflows/main.yml → ./bin/run-evals) has been red since ae077b7 [Chore] Untrack machine-local .claude state — unrelated to any feature work. The failing step is the DevMemBench benchmark run (bundle exec rspec spec/benchmarks/ --tag benchmark), not the unit suite (bundle exec rake, which is green).

Root cause

The signal-health benchmark (spec/benchmarks/health/database_signal_spec.rb) asserts contracts against the live committed .claude/memory.sqlite3 (the gem's own dogfood DB). Its before(:all) guard skipped the suite only when the file existed but wasn't a SQLite file — i.e. an unresolved git-lfs pointer on CI's lfs: false checkout.

ae077b7 untracked the DB, so on CI it is now absent entirely:

• File.exist?(project_db) → false → the guard is bypassed (never skips).
• The suite runs against a fresh empty DB created by ensure_project!.
• "has more than 5 active project facts (sanity floor)" fails: "only 0 active project facts; suspect ingest broken or DB nuked".
• rspec … --tag benchmark exits 1 → bin/run-evals prints SOME CHECKS FAILED (exit code: 1).

Fix

Skip the suite unless the DB is present AND a real SQLite file, covering both the absent (untracked/gitignored/fresh-clone) and lfs-pointer cases. These contracts only mean something against the live DB — they still run locally where it exists.

Verification

Reproduced and fixed by pointing CLAUDE_PROJECT_DIR/CLAUDE_CONFIG_DIR at empty dirs (CI's absent-DB condition):

• Before: 10 examples, 1 failure (the sanity floor).
• After: 10 examples, 0 failures, 10 pending (all skip).
• LFS-pointer case (present-but-not-SQLite) also skips.
• A present live DB still runs the suite (local validation unchanged).
• Full DB/embedding-independent benchmark subset (health + resolution + fts5 + relevance) under absent-DB: 28 examples, 0 failures.

CI on this PR is the authoritative end-to-end check (it has working fastembed + the real absent-DB checkout). One-file change; no production code touched.

Note: the eval-scenario X/7 [FAIL] lines in bin/run-evals output are a cosmetic display artifact (it counts skipped real-mode examples as non-passed); they do not drive the exit code — only the benchmark step did. Left as-is to keep this fix minimal.