fix: expand CONTRIBUTING.md with setup, workflow, and guidelines

Add getting started, development workflow, code style summary,
database change guidance, and dependency management sections.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

CONTRIBUTING.md

@@ -1,5 +1,34 @@
 # Contributing
 
+## Getting Started
+
+```bash
+git clone https://github.com/nearai/ironclaw.git
+cd ironclaw
+./scripts/dev-setup.sh
+```
+
+This installs the Rust toolchain, WASM targets, git hooks, and runs initial checks.
+
+## Development Workflow
+
+```bash
+cargo fmt                                                    # format
+cargo clippy --all --benches --tests --examples --all-features  # lint (zero warnings)
+cargo test                                                   # unit tests
+cargo test --features integration                            # + PostgreSQL tests
+```
+
+## Code Style
+
+- Zero clippy warnings policy
+- No `.unwrap()` or `.expect()` in production code (tests are fine)
+- Use `thiserror` for error types, map errors with context
+- Prefer `crate::` for cross-module imports
+- Comments for non-obvious logic only
+
+See `CLAUDE.md` for full style guidelines.
+
 ## Feature Parity Requirement
 
 When your change affects a tracked capability, update `FEATURE_PARITY.md` in the same branch.
@@ -21,3 +50,11 @@ All PRs follow a risk-based review process:
 | **C** | Security (`src/safety/`, `src/secrets/`), runtime (`src/agent/`, `src/worker/`), database schema, CI workflows | 2 approvals + rollback plan documented |
 
 Select the appropriate track in the PR template based on what your changes touch.
+
+## Database Changes
+
+IronClaw uses dual-backend persistence (PostgreSQL + libSQL). All new persistence features must support both backends. See `src/db/CLAUDE.md`.
+
+## Adding Dependencies
+
+Run `cargo deny check` before adding new dependencies to verify license compatibility and check for known advisories.