perf(docker): optimize dependency layer caching and update dockerignore

- Copy requirements.txt before application source to leverage Docker layer caching
- Expand .dockerignore to exclude local venv, cache files, logs, and .env files

.dockerignore

@@ -1,25 +1,58 @@
-**/__pycache__
-**/.classpath
-**/.dockerignore
-**/.env
+# Git
 **/.git
 **/.gitignore
+
+# Python bytecode & cache
+**/__pycache__
+**/*.py[cod]
+**/*$py.class
+**/.pytest_cache
+**/.coverage
+**/htmlcov
+
+# Virtual environments & environment files
+**/venv*
+**/.venv*
+**/env*
+**/.env*
+
+# Local databases and runtime data
+**/*.sqlite3*
+**/*.log
+**/console/cert.pem*
+**/dhcpd.*
+
+# IDEs and OS
+**/.idea
+**/.vscode
+**/.vs
+**/.DS_Store
+**/.classpath
 **/.project
 **/.settings
 **/.toolstarget
-**/.vs
-**/.vscode
 **/*.*proj.user
 **/*.dbmdl
 **/*.jfm
-**/azds.yaml
-**/bin
-**/charts
-**/docker-compose*
+**/.vagrant
+
+# Docker and CI
+**/.dockerignore
 **/Dockerfile*
+**/docker-compose*
+**/azds.yaml
+**/charts
+**/secrets.dev.yaml
+**/values.dev.yaml
+
+# Node / frontend build leftovers
 **/node_modules
 **/npm-debug.log
 **/obj
-**/secrets.dev.yaml
-**/values.dev.yaml
-README.md
+**/bin
+
+# Documentation / metadata
+README.md
+AGENTS.md
+CODEBASE_OVERVIEW.md
+DEPENDENCY_UPGRADE_PLAN.md