Stabilize GitHub Actions for monorepo CI/deploy with adaptive scope and self-healing retries

[Copilot]

This update hardens PromptOS CI/CD workflows for flaky monorepo conditions (pnpm + Turbo + TypeScript) while preserving existing job intent and core commands. It adds adaptive execution, retry/recovery behavior, stronger safety controls, and better failure observability for both CI and web deploy paths.

• CI resilience + adaptive scope (.github/workflows/ci.yml)

  • Added workflow_dispatch control (force_full_run) for manual override.
  • Added detect-changes gating via path filters to run lint/build only when relevant on PRs.
  • Added runtime auto-detection for Node (.nvmrc fallback) and pnpm (packageManager fallback).
  • Added retry + cache-recovery flow around install/type-check/lint/build (including backoff and pnpm store prune).
  • Added failure artifact uploads and structured $GITHUB_STEP_SUMMARY output.
  • Tightened concurrency grouping and explicit least-privilege job permissions.

• Deploy robustness + guardrails (.github/workflows/deploy-web.yml)

  • Expanded workflow_dispatch inputs (ref, force_deploy, notify_on_failure) for controlled manual deployments.
  • Added retries for Vercel CLI install, env pull, build, and deploy (deploy uses backoff loop).
  • Added post-deploy health check against emitted deployment URL.
  • Added failure artifact upload + optional webhook notification (CI_FAILURE_WEBHOOK).
  • Kept deployment environment wiring and output contract intact (steps.deploy.outputs.url).

• Dependabot + maintenance

  • Added .github/dependabot.yml for weekly updates across GitHub Actions and npm ecosystem.
  • Included improvements.md to document stabilization decisions and operational additions.

# Example: self-healing retry pattern now used in CI/deploy
- name: Install dependencies
  id: install-deps
  continue-on-error: true
  run: pnpm install --frozen-lockfile

- name: Retry Install dependencies
  if: steps.install-deps.outcome == 'failure'
  run: |
    sleep 5
    pnpm install --frozen-lockfile