Review gandi-operations doc and reorganize how-to guides (#200)

## Summary
- **Doc review:** Reviewed `gandi-operations.md` — added `last-reviewed` frontmatter, verified all wiki-links, confirmed Pulumi state has no drift
- **Gandi reference fix:** Added missing `cv.eblu.me` CNAME row to `gandi.md` DNS records table (was present in Pulumi but undocumented)
- **Pulumi comment fix:** Updated stale `README.md` reference in `__main__.py` to point to `docs/how-to/gandi-operations.md`
- **How-to reorg:** Moved 14 how-to guides into 3 subdirectories (`deployment/`, `configuration/`, `operations/`), collapsed the Documentation and Database index sections into Configuration and Operations respectively

## Verification
- `docs-check-links` — all 180 wiki-links valid
- `docs-check-filenames` — all 90 filenames unique
- `dns-preview` — 5 resources unchanged, no drift
- All pre-commit hooks pass

## Test plan
- [ ] Verify docs site builds correctly with new paths
- [ ] Spot-check a few wiki-links from other pages to moved how-to guides

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/200

pulumi/gandi/__main__.py

@@ -8,7 +8,7 @@ This program manages DNS records for blumeops infrastructure:
 
 Authentication:
   Set GANDI_PERSONAL_ACCESS_TOKEN environment variable.
-  See README.md for PAT management instructions.
+  See docs/how-to/gandi-operations.md for PAT management instructions.
 """
 
 import os