chore: archive completed .claude/plans/ and clean up stale plans

## Problem

The `.claude/plans/` directory contains many completed plans that should be archived, and potentially stale plans that need review.

## Plans to Review

### Cloudflared MVP Plans (01-07)
```
.claude/plans/01-cloudflared-mvp.md
.claude/plans/02-external-secrets.md
.claude/plans/03-prometheus-metrics.md
.claude/plans/04-linkerd-integration.md
.claude/plans/05-network-policy.md
.claude/plans/06-enhanced-probes.md
.claude/plans/07-extensibility.md
```
**Status**: Need to assess completion status for each

### Chart Release Workflows
```
.claude/plans/chart-release-workflows/
├── 00-initial-understanding.md
├── 01-clarifying-questions.md
├── 02-challenges.md
├── 03-answers-and-decisions.md
├── 04-goal-description.md
├── 05-research-plan.md
├── adr/ # Draft ADRs - some may have been formalized
├── components/
├── infrastructure/
├── migration-plan.md
├── rulesets-index.md
├── tests/ # Test plans
├── workflow-1/ through workflow-8/
└── workflows/
```
**Status**: Chart release workflows are IMPLEMENTED. Most of these can be archived.

### Already Archived
```
.claude/plans/archive/
├── full-atomization-model.md
└── sync-with-main-workflow-plan.md
```

### Other Plans
```
.claude/plans/foo.md # Seems like a test file
.claude/plans/divergence-fix-plan.md # May be completed
.claude/plans/helm-workflow-gaps/ # May be completed
```

## Recommended Actions

1. Move completed chart-release-workflows plans to `.claude/plans/archive/chart-release-workflows/`
2. Review cloudflared MVP plans (01-07) for completion status
3. Delete `foo.md` if it's a test file
4. Verify `divergence-fix-plan.md` and `helm-workflow-gaps/` are completed
5. Update `.claude/plans/README.md` (if exists) or create one

## Notes

- Keep draft ADRs that weren't formalized - they may have useful context
- Archive, don't delete - maintains historical reference