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

mise-tasks/ai-docs

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-#MISE description="Prime AI context with key BlumeOps documentation (formerly zk-docs)"
+#MISE description="Prime AI context with key BlumeOps documentation"
 
 set -euo pipefail
 
@@ -10,15 +10,17 @@ FILES=(
     "$DOCS_DIR/tutorials/ai-assistance-guide.md"
     "$DOCS_DIR/how-to/agent-change-process.md"
     "$DOCS_DIR/index.md"
-    "$DOCS_DIR/reference/reference.md"
-    "$DOCS_DIR/how-to/how-to.md"
     "$DOCS_DIR/how-to/operations/troubleshooting.md"
-    "$DOCS_DIR/explanation/explanation.md"
     "$DOCS_DIR/explanation/architecture.md"
-    "$DOCS_DIR/tutorials/tutorials.md"
     "$DOCS_DIR/reference/tools/mise-tasks.md"
 )
 
 # Concatenate files with headers showing paths
-# Defaults are tuned for AI consumption (plain text, file headers only)
 bat --style=header --color=never --decorations=always "$@" "${FILES[@]}"
+
+# Documentation tree — replaces the old hand-curated index files
+echo ""
+echo "=== Documentation Structure ==="
+echo "All docs under $DOCS_DIR (excluding changelog.d/):"
+echo ""
+find "$DOCS_DIR" -name '*.md' -not -path '*/changelog.d/*' | sort | sed "s|$DOCS_DIR/||"