ci(benchmark): gate scenario speed relative to the runner

Before the protocol, time the frozen engine on the two-year scenario, best
of three, and fail any scenario whose mean planning time exceeds its
multiplier times that calibration. Multipliers come from development-machine
ratios with about 1.5x headroom until #286 tightens them. The 300-second
timeout stays only as a hang guard. The benchmark keeps running on push and
pull_request events because the push run gates image publication.

This replaces the absolute 300-second acceptance protocol named in #78.

Refs #285

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -85,8 +85,8 @@ jobs:
             - run: npm install --global bun@1.4.2
             - run: bun install --frozen-lockfile
             - run: bun scripts/generate-langs.js
-            - name: Unchanged benchmark protocol
-              run: timeout 300s bunx vitest run src/app/benchmark/leave-planner-benchmark.spec.ts --maxWorkers=1
+            - name: Benchmark protocol with relative gate
+              run: timeout 300s bunx vitest run src/app/benchmark/ --maxWorkers=1
 
     build:
         name: build