Review exploring-the-docs and add doc consistency checks (#112)

## Summary
- Reviewed and cleaned up exploring-the-docs tutorial: simplified wiki-links, fixed broken replication/ reference, added Related section, corrected zk-docs flags to match CLAUDE.md
- Added orphan detection to doc-links (finds docs not linked from any other doc)
- Added new doc tooling: `doc-index` (checks category index coverage), `doc-stale` (staleness report), `doc-tags` (tag inventory)
- Added `doc-index` as a pre-commit hook
- Updated use-pypi-proxy to document env-var-based proxy toggle for pip/uv
- Updated ai-assistance-guide with new doc task descriptions

## Test plan
- [ ] Run `mise run doc-links` — passes
- [ ] Run `mise run doc-index` — passes
- [ ] Run `mise run doc-stale` — informational output
- [ ] Run `mise run doc-tags` — informational output
- [ ] Pre-commit hooks pass

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/112

.pre-commit-config.yaml

@@ -110,3 +110,9 @@ repos:
         language: system
         files: ^docs/.*\.md$
         pass_filenames: false
+      - id: doc-index
+        name: doc-index
+        entry: mise run doc-index
+        language: system
+        files: ^docs/.*\.md$
+        pass_filenames: false