Fix spider trap: disable SPA mode, remove index files, relax wiki-links (#290)

## Summary

Fixes the Facebook crawler spider trap that's been generating infinite recursive URLs like `/how-to/tutorials/tutorials/how-to/explanation/...` for several days.

**Root cause:** Quartz SPA mode + nginx `try_files` fallback to `index.html` meant any fabricated URL returned the root HTML shell with HTTP 200. Crawlers followed relative links from those fake URLs, creating infinite recursion.

**Fix:**
- Disable Quartz SPA mode (`enableSPA: false`) — all pages are now fully static HTML
- Replace nginx SPA fallback with `=404` + Quartz's static `404.html`
- Remove `robots.txt` exclusions (no longer needed)

**Docs cleanup (Obsidian.nvim compat no longer needed):**
- Delete hand-curated category index files (`tutorials.md`, `reference.md`, `how-to.md`, `explanation.md`) — Quartz auto-generates folder pages
- Delete `postgresql-storage.md` (redirect stub) and `migrate-forgejo-from-brew.md` (stale history)
- Drop `docs-check-index` and `docs-check-filenames` prek hooks
- Rewrite `docs-check-links` to allow path-based wiki-links (`[[path/to/file]]`) and only error on true ambiguity
- Add `ai-docs` doc tree listing to replace index files for AI context
- Add natural cross-links from reference cards to fix orphan docs

## Deployment and Testing

- [ ] Merge and let the build pipeline run
- [ ] Verify docs.eblu.me serves pages correctly with full page loads
- [ ] Verify non-existent URLs return 404
- [ ] Monitor crawler traffic — should drop to near zero for fabricated URLs

Reviewed-on: #290

docs/tutorials/ai-assistance-guide.md

@@ -91,7 +91,7 @@ BlumeOps operations are driven by mise tasks. Run `mise tasks` to list all avail
 
 | Task | When to Use |
 |------|-------------|
-| `ai-docs` | At session start - review infrastructure documentation |
+| `ai-docs` | At session start - review infrastructure documentation (see [[mise-tasks]]) |
 | `docs-mikado` | View active Mikado dependency chains for C2 changes |
 | `docs-mikado --resume` | Resume a C2 chain: detect branch, show state and next steps |
 | `provision-indri` | Deploy changes to [[indri]]-hosted services via Ansible |
@@ -104,9 +104,7 @@ BlumeOps operations are driven by mise tasks. Run `mise tasks` to list all avail
 | `dns-up` | Apply DNS changes via Pulumi |
 | `tailnet-preview` | Preview Tailscale ACL changes |
 | `tailnet-up` | Apply Tailscale ACL changes via Pulumi |
-| `docs-check-links` | Validate wiki-links in documentation (includes orphan detection) |
-| `docs-check-index` | Check every doc is referenced in its category index |
-| `docs-check-filenames` | Check for duplicate doc filenames |
+| `docs-check-links` | Validate wiki-links resolve correctly (supports path-based links, orphan detection) |
 | `docs-review-stale` | Report docs by last-modified date, highlight stale ones |
 | `docs-review-tags` | Print frontmatter tag inventory across all docs |
 | `docs-review` | Review the most stale doc by last-reviewed date |
@@ -120,7 +118,7 @@ For ArgoCD operations, use the `argocd` CLI directly:
 
 For AI agents building context:
 
-- [[reference|Reference]] - Entry point for technical details
+- [Reference](/reference/) - Entry point for technical details
 - [[hosts|Host Inventory]] - What hardware exists
 - [[apps|ArgoCD Apps]] - What's deployed in Kubernetes
 - [[routing|Routing]] - How services are exposed