# issue-14-documentation-and-polish: Add API documentation and README with usage examples

## Description
Add comprehensive /// doc comments to all public APIs across all modules, create a README.md with project description, installation instructions, usage examples, and DSL syntax reference. Ensure cargo doc builds cleanly, and verify all code is formatted (cargo fmt) and passes clippy lints.

## Architecture Reference
This issue spans all modules. For documentation content, refer to:
- Architecture document Section: All component public interfaces (Components 1-10) for API signatures to document
- PRD Section: Product Description, DSL Syntax (lines 159-170), CLI Commands (lines 171-180) for README content
- PRD Appendix: Example DSL Syntax (lines 329-360) for usage examples

## Interface Contracts
No new code interfaces. This issue modifies existing code to add:
```rust
/// Doc comments on all public types, functions, and modules
/// Example format:
/// /// Tokenize input DSL text into positioned tokens
/// /// Returns vector of tokens with source positions for error reporting
/// pub fn tokenize(&mut self) -> Result<Vec<PositionedToken>, DiagramError>
```

## Isolation Context
- Available: All completed modules from all prior issues (already merged)
- NOT available: None (final polish issue)
- Source of truth: Architecture document at `/Users/santoshkumarradha/Documents/agentfield/code/int-agentfield-examples/af-swe/example-diagrams/.artifacts/plan/architecture.md`

## Files
- **Create**: `README.md`
- **Modify**: `src/types.rs`, `src/error.rs`, `src/lexer.rs`, `src/parser.rs`, `src/validator.rs`, `src/layout.rs`, `src/svg.rs`, `src/ascii.rs`, `src/app.rs`, `src/cli.rs`

## Dependencies
- issue-01 (types-module)
- issue-02 (error-module)
- issue-03 (lexer-module)
- issue-04 (parser-module)
- issue-05 (validator-module)
- issue-06 (layout-module)
- issue-09 (svg-renderer)
- issue-10 (ascii-renderer)
- issue-11 (app-module)
- issue-12 (cli-module)

## Provides
- Complete API documentation for all public interfaces
- User-facing README with installation and usage examples
- Code formatting compliance (cargo fmt)
- Clippy lint compliance (cargo clippy)

## Acceptance Criteria
- [ ] README.md exists with project description, usage examples, DSL syntax reference
- [ ] README.md includes installation instructions (cargo build --release)
- [ ] README.md shows examples of compile, preview, and validate commands
- [ ] All public types in src/types.rs have /// doc comments
- [ ] All public functions in all modules have /// doc comments
- [ ] cargo doc --no-deps builds without warnings
- [ ] cargo doc --no-deps 2>&1 | grep -q 'Documenting diagrams'
- [ ] cargo fmt --check exits 0 (all code formatted)
- [ ] cargo clippy -- -D warnings exits 0 (no clippy warnings)
- [ ] ! cargo doc --no-deps 2>&1 | grep -i 'warning'

## Testing Strategy

### Verification Commands
- Build docs: `cargo doc --no-deps`
- Check formatting: `cargo fmt --check`
- Check lints: `cargo clippy -- -D warnings`
- Verify README: `test -f README.md && wc -l README.md` (should be >50 lines)

### Documentation Coverage
- **Types module**: All public types (SourcePosition, NodeType, Node, Connection, Diagram, Point, PositionedNode, PositionedConnection, LayoutDiagram)
- **Error module**: All error types (DiagramError, SyntaxError, SemanticError, IoError) and methods (exit_code, format_detailed)
- **Lexer module**: Token, PositionedToken, Lexer, tokenize method
- **Parser module**: Parser, parse method
- **Validator module**: Validator, validate method
- **Layout module**: LayoutEngine, layout method
- **SVG module**: SvgRenderer, render method
- **ASCII module**: AsciiRenderer, render method
- **App module**: App, compile/preview/validate methods
- **CLI module**: Cli, Commands enum

### Manual Verification
- Manually test README examples by copying commands and verifying they work
- Review generated cargo doc output in browser (target/doc/diagrams/index.html)
