chore: reorganize repository structure

- Move docker-compose files to .docker/compose/
- Move docker-entrypoint.sh to .docker/
- Move DOCKER.md to .docker/README.md
- Move 16 implementation docs to docs/implementation/
- Delete test artifacts (block_test.txt, caddy_*.json)
- Update all references in Dockerfile, Makefile, tasks, scripts
- Add .github/instructions/structure.instructions.md for enforcement
- Update CHANGELOG.md

Root level reduced from 81 items to ~35 visible items.

.gitignore

@@ -212,5 +212,24 @@ import/
 test-results/charon.hatfieldhosted.com.har
 test-results/local.har
 .cache
-trivy-scan-output.txt
-trivy-image-scan.txt
+
+# -----------------------------------------------------------------------------
+# Test artifacts at root
+# -----------------------------------------------------------------------------
+/block*.txt
+/final_block_test.txt
+
+# -----------------------------------------------------------------------------
+# Debug/temp config files at root
+# -----------------------------------------------------------------------------
+/caddy_*.json
+
+# -----------------------------------------------------------------------------
+# Trivy scan outputs at root
+# -----------------------------------------------------------------------------
+/trivy-*.txt
+
+# -----------------------------------------------------------------------------
+# Docker Overrides (new location)
+# -----------------------------------------------------------------------------
+.docker/compose/docker-compose.override.yml