chore: migrate development environment from Nix flakes to devenv

Replace Nix flake-based development setup with devenv for better
developer experience and more streamlined environment management.

Changes:
  - Remove flake.nix and flake.lock files
  - Add devenv.nix, devenv.yaml, and devenv.lock configuration
  - Update .envrc to use devenv instead of nix develop
  - Remove Docker development setup (compose.dev.yml, docker/mod.just)
  - Expand .gitignore with comprehensive IDE and OS exclusions
  - Remove Docker-related just commands from justfile

.gitignore

@@ -2,3 +2,54 @@
 .env
 /coverage
 /target
+
+# Devenv
+.devenv*
+devenv.local.nix
+
+# direnv
+.direnv
+
+# pre-commit
+.pre-commit-config.yaml
+
+# Emacs backup files
+*~
+\#*\#
+.\#*
+
+# Vim files
+*.swp
+*.swo
+*~
+
+# VS Code
+.vscode/
+*.code-workspace
+
+# JetBrains IDEs
+.idea/
+*.iml
+
+# macOS
+.DS_Store
+.AppleDouble
+.LSOverride
+
+# Windows
+Thumbs.db
+ehthumbs.db
+Desktop.ini
+
+# Linux
+*~
+
+# Temporary files
+*.tmp
+*.temp
+*.log
+
+# OS generated files
+.Spotlight-V100
+.Trashes
+._*