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/exploring-the-docs.md

@@ -18,18 +18,18 @@ The docs follow the [Diataxis](https://diataxis.fr/) framework:
 
 | Section | Purpose | When to Use |
 |---------|---------|-------------|
-| **[[tutorials|Tutorials]]** | Learning-oriented | "I'm new and want to understand" |
-| **[[reference|Reference]]** | Information-oriented | "I need specific technical details" |
-| **[[how-to|How-to]]** | Task-oriented | "I need to do X" |
-| **[[explanation|Explanation]]** | Understanding-oriented | "I want to understand why" |
+| **[Tutorials](/tutorials/)** | Learning-oriented | "I'm new and want to understand" |
+| **[Reference](/reference/)** | Information-oriented | "I need specific technical details" |
+| **[How-to](/how-to/)** | Task-oriented | "I need to do X" |
+| **[Explanation](/explanation/)** | Understanding-oriented | "I want to understand why" |
 
 ## Quick Paths by Audience
 
 ### For Erich (Owner)
 
 You probably want quick access to operational details:
-- [[how-to]] guides for common operations (deploy, troubleshoot, update ACLs)
-- [[reference]] has service URLs, commands, and config locations
+- [How-to](/how-to/) guides for common operations (deploy, troubleshoot, update ACLs)
+- [Reference](/reference/) has service URLs, commands, and config locations
 - [[ai-assistance-guide]] explains how to work effectively with Claude
 - Run `mise run ai-docs` to prime AI context with key documentation
 
@@ -37,40 +37,41 @@ You probably want quick access to operational details:
 
 Context for effective assistance:
 - Read [[ai-assistance-guide]] for operational conventions
-- [[reference]] has the technical specifics you'll need
+- [Reference](/reference/) has the technical specifics you'll need
 - The repo's `CLAUDE.md` has critical rules (especially the kubectl context requirement)
 
 ### For External Readers
 
 Understanding what this is:
-- [[explanation]] covers the "why" behind design decisions
-- [[reference]] shows what's actually running
+- [Explanation](/explanation/) covers the "why" behind design decisions
+- [Reference](/reference/) shows what's actually running
 - Browse service pages to see specific implementations
 
 ### For Contributors
 
 Getting started with changes:
 - [[contributing]] walks through the workflow
-- [[how-to]] guides for specific tasks (deploy services, add roles)
-- [[reference]] tells you where things live
+- [How-to](/how-to/) guides for specific tasks (deploy services, add roles)
+- [Reference](/reference/) tells you where things live
 
 ### For Replicators
 
 Replicators are people who want to build their own similar homelab GitOps setup, using BlumeOps as inspiration.
 
 - [[replicating-blumeops]] provides the overview, with linked tutorials that go deep on individual components
-- [[explanation]] covers architecture and design rationale
+- [Explanation](/explanation/) covers architecture and design rationale
 - Reference pages show specific configuration choices
 
 ## Using Wiki Links
 
 Documentation uses `[[wiki-links]]` for cross-references:
-- `[[service-name]]` links to a reference page
+- `[[service-name]]` links by filename stem (must be unambiguous)
+- `[[path/to/file]]` links by path from docs root (for disambiguation)
 - `[[page|Display Text]]` customizes the link text
 
 When reading on the web (docs.eblu.me), these render as clickable links. The backlinks panel shows what references each page.
 
-Prek hooks automatically validate that all wiki-links point to existing files and that link targets are unambiguous.
+Prek hooks validate that all wiki-links resolve to existing files and flag ambiguous bare-name links.
 
 ## AI Context Priming
 
@@ -80,10 +81,9 @@ The `ai-docs` mise task concatenates key documentation files for AI context:
 mise run ai-docs
 ```
 
-This outputs the AI assistance guide, reference index, how-to index, architecture overview, and tutorials index in plain text with file headers - providing Claude with essential context for BlumeOps operations.
+This outputs key documentation files and a full tree listing of all docs, providing Claude with essential context for BlumeOps operations.
 
 ## Related
 
-- [[tutorials]] - Parent index of all tutorials
 - [[update-documentation]] - How to publish doc changes
 - [[review-documentation]] - Periodic doc review process