chore: improve .gitignore coverage

Add .env.* pattern with \!.env.example exception, *.sqlite3, and
testing artifacts (.coverage, .pytest_cache/, htmlcov/, .mypy_cache/).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: marc-shade

.gitignore

@@ -24,6 +24,8 @@ MANIFEST
 # Sensitive Files and Secrets
 *.env
 .env
+.env.*
+!.env.example
 *.secret
 *.key
 *.pem
@@ -52,6 +54,7 @@ bump_version.py
 # Logs and Databases
 *.log
 *.sqlite
+*.sqlite3
 *.db
 
 # Virtual Environment
@@ -69,6 +72,12 @@ document_context.md
 .idea/
 .vscode/
 
+# Testing
+.coverage
+.pytest_cache/
+htmlcov/
+.mypy_cache/
+
 # OS
 .DS_Store
 Thumbs.db