feat(scripts): add readme_generator — auto-generate README from codebase

Adds scripts/readme_generator.py — a tool that scans Python codebases,
extracts module docstrings, entry points (argparse main), and directory
structure to generate a standard README.md with: description, installation,
usage, scripts list.

Acceptance for #97:
- Reads codebase structure (AST-based Python file scanner)
- Generates README sections (Description, Installation, Usage, Scripts, Directory)
- Updates existing README (replaces on run — idempotent)
- 1 per run (single repo per invocation)

Usage:
    python3 scripts/readme_generator.py              # generate in-place
    python3 scripts/readme_generator.py --dry-run    # preview stats
    python3 scripts/readme_generator.py --dir /path

Closes #97

scripts/readme_generator.py

@@ -0,0 +1,152 @@
+#!/usr/bin/env python3
+"""
+README Generator — Scan codebase and generate/update README.md.
+
+Reads codebase structure, extracts module docstrings and main entry points,
+produces a README with: description, installation, usage, API/scripts list.
+
+Usage:
+    python3 scripts/readme_generator.py
+    python3 scripts/readme_generator.py --dir /path/to/repo
+    python3 scripts/readme_generator.py --dry-run  # preview without writing
+"""
+import argparse
+import ast
+import json
+import sys
+from pathlib import Path
+from typing import List, Dict, Optional
+
+def read_file(path: Path) -> str:
+    try:
+        return path.read_text()
+    except Exception:
+        return ""
+
+def extract_module_docstring(path: Path) -> str:
+    try:
+        tree = ast.parse(read_file(path))
+        return ast.get_docstring(tree) or ""
+    except Exception:
+        return ""
+
+def extract_parser_description(path: Path) -> str:
+    """Extract the first ArgumentParser description found in the file."""
+    try:
+        content = read_file(path)
+        for line in content.split('\n'):
+            if 'ArgumentParser' in content[max(0,content.index(line)-100):content.index(line)+200] and 'description=' in line:
+                desc_part = line.split('description=')[1]
+                desc = desc_part.strip().rstrip(',').strip('"\'')
+                return desc
+        return ""
+    except Exception:
+        return ""
+
+def scan_python_files(root: Path) -> List[Dict]:
+    """Collect Python files (exclude tests) with basic metadata."""
+    files = []
+    for path in root.rglob('*.py'):
+        rel = path.relative_to(root)
+        parts = rel.parts
+        if any(p.startswith('test_') or p in ('__pycache__', '.git', 'venv', '.venv', '.pytest_cache') for p in parts):
+            continue
+        files.append({
+            'path': str(rel),
+            'docstring': extract_module_docstring(path),
+            'parser_desc': extract_parser_description(path),
+            'name': path.name,
+        })
+    return sorted(files, key=lambda x: x['path'])
+
+def detect_entry_point(file_info: Dict) -> bool:
+    """A file is an entry point if it has a main block or argparse."""
+    path = Path(file_info['path'])
+    name = path.name
+    return name in ('__main__.py', 'main.py') or bool(file_info['parser_desc']) or path.parts[0] == 'bin'
+
+def generate_readme(root_dir: str, output_path: Optional[str] = None, dry_run: bool = False) -> str:
+    root = Path(root_dir).resolve()
+    py_files = scan_python_files(root)
+    
+    sections = []
+    repo_name = root.name
+    
+    sections.append(f"# {repo_name}\n")
+    
+    if py_files:
+        main_doc = py_files[0]['docstring'].strip()
+        if main_doc:
+            sections.append(main_doc + "\n")
+        else:
+            sections.append("A Python project.\n")
+    else:
+        sections.append("A Python project.\n")
+    
+    sections.append("## Installation\n")
+    if (root / "requirements.txt").exists():
+        sections.append("```bash\ncp .env.example .env  # if present\npip install -r requirements.txt\n```\n")
+    elif (root / "pyproject.toml").exists():
+        sections.append("```bash\npip install -e .\n```\n")
+    else:
+        sections.append("```bash\npip install -e .\n```\n")
+    
+    sections.append("## Usage\n")
+    entry_scripts = [f for f in py_files if detect_entry_point(f)]
+    if entry_scripts:
+        for f in entry_scripts[:8]:
+            name = f['name']
+            if f['parser_desc']:
+                sections.append(f"### {name}\n{f['parser_desc']}\n")
+            else:
+                sections.append(f"### {name}\n```bash\npython3 {f['path']}\n```\n")
+    else:
+        sections.append("See `scripts/` directory for available tools.\n")
+    
+    sections.append("## Scripts\n")
+    if entry_scripts:
+        for f in entry_scripts[:15]:
+            desc = f['docstring'].strip().split('\n')[0] if f['docstring'].strip() else "Utility script."
+            sections.append(f"- **{f['name']}**: {desc}")
+    else:
+        sections.append("- No entry-point scripts detected.\n")
+    
+    sections.append("\n## Directory Structure\n")
+    top_dirs = sorted([
+        d.name for d in root.iterdir()
+        if d.is_dir() and not d.name.startswith('.') and d.name not in ('__pycache__', 'venv', '.venv', 'node_modules')
+    ])
+    sections.append("```\n")
+    for d in top_dirs[:12]:
+        sections.append(f"{d}/")
+    sections.append("```\n")
+    
+    readme_content = "\n".join(sections)
+    
+    if dry_run:
+        print(json.dumps({
+            "repo": repo_name,
+            "sections": len(sections),
+            "chars": len(readme_content),
+            "python_files": len(py_files),
+            "entry_scripts": sum(1 for f in py_files if detect_entry_point(f)),
+        }, indent=2))
+        return ""
+    
+    if output_path is None:
+        output_path = root / "README.md"
+    else:
+        output_path = Path(output_path)
+    
+    output_path.write_text(readme_content)
+    print(f"README {'updated' if output_path.exists() else 'created'}: {output_path} ({len(readme_content)} bytes)")
+    return str(output_path)
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(description="Generate or update README.md from codebase structure.")
+    parser.add_argument("--dir", default=".", help="Directory to scan (default: current)")
+    parser.add_argument("--output", help="Output README path (default: README.md in scanned dir)")
+    parser.add_argument("--dry-run", action="store_true", help="Preview without writing")
+    args = parser.parse_args()
+    
+    generate_readme(args.dir, args.output, args.dry_run)