feat: cross-model consensus consolidation (one ranked comment, not N walls)

With >=2 models the swarm now posts ONE consensus comment instead of a
per-model comment each. Every model writes its structured findings to a shared
dir (GADFLY_FINDINGS_OUT); after the swarm finishes, a consolidation pass
(the binary in GADFLY_CONSOLIDATE_DIR mode) clusters findings by location
(±3 lines), counts how many models independently flagged each, escalates to the
highest reported severity, and renders an agreement-ranked table — cross-model
agreement being the strongest real-vs-false-positive signal we have.

- consensus.go: modelFindings artifact, collectFindings (shared with emit),
  writeFindingsOut, runConsolidate, clustering + renderConsensus. Lone
  low-severity findings fold away; a lone critical still surfaces; each model's
  full review is preserved folded inside the one comment.
- main.go: GADFLY_CONSOLIDATE_DIR dispatches to consolidation; writeFindingsOut
  after a normal review.
- emit.go: reuse collectFindings (one definition of "what a finding is").
- run.sh: when GADFLY_CONSOLIDATE=1, write findings + skip the per-model comment
  (live progress still on the status board).
- entrypoint.sh: auto-enable for >=2 models; run the consolidator after the
  barrier and upsert ONE consensus comment; FALL BACK to per-model comments if
  consolidation yields nothing (advisory invariant: never lose output).
- README + reusable workflow (`consolidate` input) + entrypoint docs updated.

Tests: clustering/agreement/tolerance, severity escalation, nit folding, lone
critical, write→consolidate round-trip, empty-dir error. gofmt/vet clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/review-reusable.yml

@@ -60,6 +60,7 @@ on:
       worker_model:              { type: string, default: "" }   # GADFLY_WORKER_MODEL
       allowed_users:             { type: string, default: "" }   # GADFLY_ALLOWED_USERS (consumer-specific; set in your stub)
       trigger_phrase:            { type: string, default: "" }   # GADFLY_TRIGGER_PHRASE
+      consolidate:               { type: string, default: "" }   # GADFLY_CONSOLIDATE — "" => auto (one consensus comment for >=2 models); "0" => one comment per model
       # Job wall-clock cap. 90 as a default: the 5-lens suite across a slow lane
       # (claude-code with extended thinking) over two passes can run long.
       timeout_minutes:           { type: number, default: 90 }
@@ -143,3 +144,4 @@ jobs:
           GADFLY_WORKER_MODEL: ${{ inputs.worker_model }}
           GADFLY_ALLOWED_USERS: ${{ inputs.allowed_users }}
           GADFLY_TRIGGER_PHRASE: ${{ inputs.trigger_phrase }}
+          GADFLY_CONSOLIDATE: ${{ inputs.consolidate }}