[gh-aw-rollout] Set up GH-AW with aws- prefixed workflow infrastructure

[pulumi-bot]

Summary

This PR sets up GitHub Agentic Workflows (GH-AW) in this repository as part of the standard rollout, using aws- workflow ID prefixes.

Commands Executed

gh aw version                          # → v0.53.1
gh aw init                             # Initialized repo for agentic workflows
gh aw compile                          # Skipped — no .md workflow files present (see blocker below)
gh aw validate                         # Skipped — no .md workflow files present (see blocker below)
```

**Final AW entrypoint used:** `gh aw` (v0.53.1)

## Changed Files

| File | Change |
|------|--------|
| `.gitattributes` | Added by `gh aw init` — marks `*.lock.yml` as generated/merge=ours |
| `.github/agents/agentic-workflows.agent.md` | Added by `gh aw init` — dispatcher agent for workflow tasks |
| `.github/workflows/aws-validate-agentic-workflows.yml` | New — validates and compiles agentic workflows on PR/push to main |
| `.github/workflows/copilot-setup-steps.yml` | Added by `gh aw init` — configures Copilot Agent with gh-aw MCP server |
| `.vscode/mcp.json` | Added by `gh aw init` — VSCode MCP server config for gh-aw |
| `.vscode/settings.json` | Added by `gh aw init` — enables Copilot markdown support |
| `mise.toml` | Updated — pinned `gh-aw` at `0.53.1`, added `aw-version`/`aw-validate`/`aw-compile` tasks |

## Validation Outputs

`gh aw compile` and `gh aw validate` both returned:
```
✗ no markdown files found in .github/workflows
```

This is expected — the `aws-pr-review` and `aws-pr-rereview` workflow `.md` files could not be installed (see blocker below). Once those files are present, compile and validate will pass.

## ⚠️ Blocker: aws-pr-review and aws-pr-rereview not installed

The step to run:
```
gh aw add pulumi-labs/gh-aw-internal/.github/workflows/gh-aw-pr-review.md@main --name aws-pr-review --force
gh aw add pulumi-labs/gh-aw-internal/.github/workflows/gh-aw-pr-rereview.md@main --name aws-pr-rereview --force
```

failed with:
```
✗ HTTP 401: authentication token not found for host github.com

The gh CLI was not authenticated in the rollout workflow run. A valid GH_TOKEN (with read access to pulumi-labs/gh-aw-internal) must be provided to the workflow for this step to succeed. This is a known issue being addressed in pulumi/provider-ops branch fix/gh-aw-rollout-token-fallback.

Next action: Once the token issue is resolved upstream, re-run the rollout to add aws-pr-review and aws-pr-rereview workflows and their lock files.

---

Rollout triggered via provider-ops#20 — workflow run 22725415390

Generated by Generic Rollout Worker · ◷