Add pre-commit hooks for code quality

[manavgup]

Context

Borrowed from IBM/mcp-context-forge which uses .pre-commit-config.yaml with fail_fast: true.

Currently nothing prevents pushing unformatted or broken code. make check is manual.

What to do

• Add .pre-commit-config.yaml with:
  • ruff (lint + format)
  • black (formatting)
  • Python AST validity check
  • Debug statement detection (breakpoint(), pdb)
  • Private key / secrets detection
  • YAML/JSON/TOML validation
  • Trailing whitespace, end-of-file fixer
• Add pre-commit to dev dependencies
• Add make pre-commit-install target
• Document in DEVELOPING.md

Acceptance criteria

• pre-commit run --all-files passes
• Hooks auto-run on git commit

[manavgup]

Closed by PR #16