docs: retire PROJECT_GUIDELINES.md — library-visibility rule now in AGENTS.md + dev docs

PROJECT_GUIDELINES.md had drifted out of reality (podman-only rule
while the stack runs docker; verifier scripts wired to Makefile targets
nobody runs). Trashed it, its two verifier scripts, and the Makefile
targets; the rules that still matched reality (docker runtime, schema
in place until release, server binary only via Docker, services layer,
integration-test pool rules) are absorbed into the new AGENTS.md.

The library-visibility family-lens rule now has a real home:
- AGENTS.md: the standing rule agents auto-discover (new media
  endpoints MUST thread the visible-library set; 403, never silently
  pass; history of the 2026-10-13 leak).
- docs/developer/library-visibility.md: the full explanation (helpers,
  SQL pattern, per-item content gates, series per-library), linked
  from the developer docs index.
Stale doc links updated (docs index, contributing, development).

Makefile

@@ -1,4 +1,3 @@
-.PHONY: help test test-integration test-all rebuild rebuild-force rebuild-app rebuild-app-force rebuild-force-db clean restart up down logs ps test-env-up test-env-down verify-guidelines verify-quick release
 
 # Include .env file for environment variables (single source of truth)
 # Ignore if .env doesn't exist yet
@@ -42,8 +41,6 @@ help:
 	@echo "  make test-env-down     - Stop test environment"
 	@echo ""
 	@echo "Verification:"
-	@echo "  make verify-guidelines - Run comprehensive guidelines check"
-	@echo "  make verify-quick      - Run quick guidelines check"
 	@echo ""
 	@echo "Release:"
 	@echo "  ./release v0.3.0            - Tag, push, and release (notes auto-generated from commits)"
@@ -153,14 +150,7 @@ test-env-up:
 test-env-down:
 	$(COMPOSE) down -v
 
-# Verify project guidelines compliance
-verify-guidelines:
-	@echo "Running comprehensive project guidelines verification..."
-	@./scripts/verify-guidelines.sh
 
-verify-quick:
-	@echo "Running quick project guidelines verification..."
-	@./scripts/verify-quick.sh
 
 # Create an annotated version tag carrying auto-generated release notes (git-cliff)
 # and push it. The tag push triggers .gitea/workflows/release.yml, which builds the