Set up Husky pre-commit hooks with lint-staged configuration to
automatically run formatting and linting on staged files before
commits. This ensures code quality by running:
- Prettier and ESLint on JS/TS files
- Cargo fmt and clippy on Rust files

Updated README with developer setup instructions.

Issue: BTC-2650

Co-authored-by: llm-git <llm-git@ttll.de>

Add Rust linting configuration to check for unexpected cfg conditions
from dependencies. Fix multiple clippy warnings including:

- Replace map().unwrap_or(false) with simpler expressions
- Use *cached instead of clone() for XpubTriple
- Use x_only_public_key() instead of to_inner()
- Simplify control flow with div_ceil() and find()
- Avoid unnecessary cloning with tap_script_sigs.insert(*key, *sig)
- Add #[allow(clippy::too_many_arguments)] where appropriate

Issue: BTC-2650

Co-authored-by: llm-git <llm-git@ttll.de>