chore(ci): cost optimization audit – please review and apply fixes

[iamdrewfortini]

This PR adds CI audit artifacts for repository-scoped cost optimization and invites the @claude agent to propose and apply fixes.

What’s included:

• .github/ci-audit/workflows-audit.json – per-repo summary of failing runs and job metadata
• .github/ci-audit/cost-hints.md – prioritized hints to reduce CI costs (timeouts, path filters, concurrency, schedules)

@claude please:

1. Read .github/ci-audit/workflows-audit.json and .github/ci-audit/cost-hints.md
2. Propose concrete changes to .github/workflows/*.yml to reduce cost (skip docs-only, add path filters, set concurrency, cancel-in-progress, increase cache hit rate, reduce matrix)
3. Apply changes directly in this PR (write access) and explain each change briefly in a review comment

[iamdrewfortini]

Suggested baseline cost optimizations for workflows (apply where appropriate):

• Add concurrency (cancel duplicates):

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

• Skip non-code changes:

on:
  push:
    paths-ignore:
      - '**/*.md'
      - '.github/ci-audit/**'

• Add timeouts to long-running jobs:

jobs:
  build:
    timeout-minutes: 20