docs: ADR index has inconsistencies with actual implementations

## Problem

The ADR index in `docs/src/adr/index.md` has some inconsistencies and missing ADRs.

## Issues Found

### 1. ADR-006 Supersession Note is Confusing
The index shows:
```
| ADR-006 | Release-Please for Helm Chart Versioning | Superseded by ADR-003 |
```

But ADR-003 is "Semantic Versioning with git-cliff" - the supersession relationship isn't immediately clear.

**Recommendation**: Update ADR-003 title to be more explicit about replacing release-please, or add a note.

### 2. Missing ADRs from SUMMARY.md
The `docs/src/SUMMARY.md` is missing entries for:
- ADR-008: Repository Dispatch for Workflow Automation
- ADR-009: Trust-Based Auto-Merge for Integration Branch

These exist in the index but aren't linked in the book navigation.

### 3. ADR-005 vs Workflow Architecture Doc
ADR-005 (CI/CD Workflow Architecture) and `docs/src/ci/workflow-architecture.md` overlap significantly. Consider consolidating or clarifying the relationship.

## Recommended Changes

1. Sync SUMMARY.md with ADR index - add missing ADR links
2. Clarify ADR-006/ADR-003 relationship in titles or notes
3. Review ADR-005 vs workflow-architecture.md for duplication

## Related
- Part of documentation refresh for chart release workflows