chore: add commit conventions

- add simple commit message format
- only 8 types: feat, fix, docs, style, refactor, test, perf, chore
- max 50 chars, lowercase, no scope
- add .gitmessage template

.gitmessage

@@ -0,0 +1,14 @@
+# <type>: <description>
+# 
+# Types: feat, fix, docs, style, refactor, test, perf, chore
+# 
+# Examples:
+# feat: add tree-sitter parser
+# fix: handle nil input  
+# test: add parser tests
+# 
+# Rules:
+# - Max 50 chars
+# - Start with lowercase
+# - No period at end
+# - No scope (no "feat(parser):")

docs/COMMIT_CONVENTION.md

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+# Commit Message Convention
+
+## Format
+
+```
+<type>: <description>
+
+[optional body]
+
+[optional footer]
+```
+
+## Rules
+
+1. **Keep it short**: First line max 50 characters
+2. **No scope needed**: Keep it simple
+3. **Lowercase**: Start description with lowercase
+4. **No period**: No period at the end
+5. **Imperative mood**: "add" not "added" or "adds"
+
+## Types (only these 8)
+
+- `feat:` - New feature
+- `fix:` - Bug fix  
+- `docs:` - Documentation only
+- `style:` - Formatting, no code change
+- `refactor:` - Code restructuring
+- `test:` - Add/update tests
+- `perf:` - Performance improvement
+- `chore:` - Maintenance, dependencies
+
+## Examples
+
+### Simple (preferred)
+```
+feat: add tree-sitter parser
+fix: handle nil input
+docs: update readme
+test: add parser tests
+refactor: simplify cfg logic
+chore: update dependencies
+```
+
+### With body (when necessary)
+```
+fix: correct loop handling in cfg
+
+Previous implementation incorrectly connected
+break statements in nested loops.
+
+Fixes #456
+```
+
+### With breaking change
+```
+feat: change api interface
+
+BREAKING CHANGE: Parse() now returns (*AST, error)
+instead of just *AST
+```
+
+## Quick Reference
+
+```bash
+# Feature
+git commit -m "feat: add python 3.11 support"
+
+# Fix
+git commit -m "fix: handle empty files"
+
+# Docs
+git commit -m "docs: add api examples"
+
+# Test
+git commit -m "test: add benchmark tests"
+
+# Multiple changes (use body)
+git commit -m "feat: add clone detection
+
+- implement apted algorithm
+- add similarity threshold
+- add tests"
+```
+
+## DON'T
+
+❌ `feat(parser): add tree-sitter support` - No scope needed
+❌ `feat: Added parser.` - No past tense, no period
+❌ `feat: Add Parser` - No title case
+❌ `feature: add parser` - Use standard types only
+❌ `add parser` - Always include type
+
+## Automated Validation
+
+The CI will check commit messages. To test locally:
+
+```bash
+# Check last commit
+git log -1 --pretty=format:"%s" | grep -E "^(feat|fix|docs|style|refactor|test|perf|chore): [a-z]"
+```
+
+## VS Code Integration
+
+Add to `.vscode/settings.json`:
+
+```json
+{
+  "git.inputValidation": "always",
+  "git.inputValidationLength": 50,
+  "git.inputValidationSubjectLength": 50
+}
+```
+
+## Why Simple?
+
+- Faster to write
+- Easier to scan in git log
+- Less cognitive overhead
+- Focus on the change, not the format
+
+Remember: **Keep it simple, keep it consistent**