Fm/stg 956 make ci faster (#1246)

# why

CI was slow due to sequential eval jobs, repeated builds, and
inefficient dependency management.

# what changed

Parallel Execution:
- Eval jobs now run in parallel instead of sequentially (regression →
all others in parallel)
  - Reduces total CI time from ~25 mins to ~12 mins

  Build Caching:
  - Build artifacts uploaded once and reused by all eval jobs
  - Eliminates 6 redundant builds (~2-3 min savings each)

  Smart Skipping:
  - skip-evals label: skip all evals
  - skip-regression-evals label: skip regression only
  - Auto-skip for docs-only changes (not on main)

  Dependency Optimization:
  - Use pnpm/action-setup@v4 with caching
  - Use --frozen-lockfile for deterministic installs
  - Remove unnecessary node_modules cleanup

  Test Parallelization:
  - Local tests: 2→3 workers (Browserbase), 2→4 workers (standard)
  - Better CI vs local environment detection

# test plan

 - Verify build artifacts upload/download correctly
  - Confirm eval jobs run in parallel after regression
  - Test skip-evals and skip-regression-evals labels work
  - Verify docs-only changes skip evals (except on main)
  - Measure CI time reduction (~50-60% expected)
  - Confirm no test flakiness from increased parallelization
  - All tests, lint, and build pass

---------

Co-authored-by: Sean McGuire <75873287+seanmcguire12@users.noreply.github.com>

Author: filip-michalsky

.changeset/proud-olives-burn.md

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+---
+"@browserbasehq/stagehand": patch
+---
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+make ci faster