chore: add comprehensive .gitignore for cross-platform development

Add .gitignore covering:
- Operating systems: macOS, Windows, Linux
- IDEs: VSCode, JetBrains, Eclipse, Vim, Emacs
- AI editors: Claude Code, OpenCode, Cursor, Aider, etc.
- Python: venv, __pycache__, dist, coverage
- Project: generated presentations, logs, env files

.gitignore

@@ -0,0 +1,264 @@
+# ============================================
+# Operating Systems
+# ============================================
+
+# macOS
+.DS_Store
+.AppleDouble
+.LSOverride
+._*
+.DocumentRevisions-V100
+.fseventsd
+.Spotlight-V100
+.TemporaryItems
+.Trashes
+.VolumeIcon.icns
+.com.apple.timemachine.donotpresent
+.com.apple.timemachine.supported
+AppleDB
+AppleDesktop
+Network Trash Folder
+Temporary Items
+.apdisk
+
+# Windows
+Thumbs.db
+Thumbs.db:encryptable
+ehthumbs.db
+ehthumbs_vista.db
+*.stackdump
+[Dd]esktop.ini
+$RECYCLE.BIN/
+*.lnk
+*.url
+*.cab
+*.msi
+*.msix
+*.msm
+*.msp
+*.msixbundle
+*.lnk
+*.url
+
+# Linux
+*~
+.fuse_hidden*
+.directory
+.Trash-*
+.nfs*
+
+# ============================================
+# IDEs & Editors
+# ============================================
+
+# VSCode
+.vscode/
+*.code-workspace
+.history/
+
+# JetBrains IDEs (IntelliJ, PyCharm, WebStorm, CLion, etc.)
+.idea/
+*.iml
+*.ipr
+*.iws
+.idea_modules/
+out/
+*.nav
+.idea/**
+
+# Eclipse
+.project
+.classpath
+.settings/
+.metadata
+.recommenders
+bin/
+tmp/
+*.tmp
+*.bak
+*.swp
+*~.nib
+*.tmproj
+
+# Sublime Text
+*.sublime-workspace
+*.sublime-project
+
+# Vim
+*.swp
+*.swo
+*.swn
+*~
+.[!.]*.sw[a-z]
+.netrwhist
+
+# Emacs
+*~
+\#*\#
+/.emacs.desktop
+/.emacs.desktop.lock
+auto-save-list
+tramp
+.\#*
+
+# ============================================
+# Python
+# ============================================
+
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# PyInstaller
+*.manifest
+*.spec
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py,cover
+.hypothesis/
+.pytest_cache/
+
+# Virtual environments
+venv/
+env/
+ENV/
+env.bak/
+venv.bak/
+.venv/
+.virtualenv/
+pipenv/
+.virtualenvs/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+*.ipynb
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+.python-version
+
+# pipenv
+Pipfile.lock
+
+# PEP 582
+__pypackages__/
+
+# Cython debug symbols
+cython_debug/
+
+# ============================================
+# Project Specific
+# ============================================
+
+# Generated presentations
+presentations/*.pptx
+!presentations/.gitkeep
+
+# Logs
+*.log
+logs/
+
+# Database
+*.db
+*.sqlite
+*.sqlite3
+
+# Temporary files
+*.tmp
+*.temp
+*.bak
+*.cache
+
+# ============================================
+# Environment & Secrets
+# ============================================
+
+.env
+.env.*
+!.env.example
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+*.pem
+*.key
+*.cert
+secrets/
+credentials/
+
+# ============================================
+# Build & Package
+# ============================================
+
+# Node modules (if any)
+node_modules/
+
+# npm
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+package-lock.json
+yarn.lock
+pnpm-lock.yaml
+
+# ============================================
+# Misc
+# ============================================
+
+# Archives
+*.zip
+*.tar
+*.tar.gz
+*.rar
+*.7z
+
+# Large files
+*.iso
+*.dmg
+
+# OS generated files
+.Spotlight-V100
+.Trashes
+
+# ============================================
+# Keep important directories
+# ============================================
+
+# Uncomment to keep directory structure
+# !templates/
+# !examples/
+# !assets/