docs: add comprehensive onboarding documentation (#71)

- Rewrite README with quick start, CLI reference, deployment guides
- Add CONTRIBUTING.md with code standards and workflow
- Add Dockerfile for containerized deployment
- Add docker-compose.yml for local development

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: copyleftdev

CONTRIBUTING.md

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+# Contributing to zgrok
+
+## Development Setup
+
+```bash
+git clone https://github.com/copyleftdev/zgrok.git
+cd zgrok
+cargo build
+cargo test
+```
+
+## Code Standards
+
+### No Tutorial Comments
+
+Comments explaining what code does are prohibited. Code must be self-documenting.
+
+```rust
+// BAD
+let count = 0; // Initialize counter to zero
+
+// BAD
+// Loop through items and process each one
+for item in items { process(item); }
+
+// GOOD - no comment needed
+let active_connections = 0;
+for connection in connections { connection.process(); }
+
+// GOOD - explains why, not what
+// Subtract 1 because stream IDs are 1-indexed in the protocol
+let index = stream_id - 1;
+```
+
+**Allowed comments:**
+- `TODO`, `FIXME`
+- `SAFETY:` for unsafe blocks
+- Doc comments (`///`) for public APIs
+- Non-obvious "why" explanations
+
+### Error Handling
+
+- Use `thiserror` for library errors
+- Use `anyhow` for binary errors
+- No `.unwrap()` in library code
+- Propagate errors with `?`
+
+### Async
+
+- Tokio runtime
+- Prefer `async fn` over manual `Future` implementations
+- Use `tokio::select!` for concurrent operations
+
+### Imports
+
+Group in order:
+1. `std`
+2. External crates
+3. Workspace crates
+4. `crate::`
+5. `super::`, `self::`
+
+## Branch Workflow
+
+```bash
+# 1. Start from main
+git checkout main && git pull
+
+# 2. Create feature branch
+git checkout -b feat/short-description
+
+# 3. Make changes, then verify
+cargo test && cargo clippy -- -D warnings && cargo fmt --check
+
+# 4. Commit
+git add -A && git commit -m "feat(component): description"
+
+# 5. Push and create PR
+git push -u origin feat/short-description
+gh pr create --fill
+
+# 6. Merge after review
+gh pr merge --squash --delete-branch
+
+# 7. Return to main
+git checkout main && git pull
+```
+
+## Commit Messages
+
+Format: `type(scope): description`
+
+Types:
+- `feat` - New feature
+- `fix` - Bug fix
+- `refactor` - Code change that neither fixes a bug nor adds a feature
+- `docs` - Documentation only
+- `test` - Adding or fixing tests
+- `chore` - Maintenance tasks
+
+Examples:
+```
+feat(agent): add TCP tunnel support
+fix(edge): handle connection timeout gracefully
+refactor(protocol): simplify frame encoding
+```
+
+## Testing
+
+```bash
+# All tests
+cargo test
+
+# Single crate
+cargo test -p zgrok-protocol
+
+# Single test
+cargo test test_name
+
+# With output
+cargo test -- --nocapture
+```
+
+Write tests alongside code in `#[cfg(test)]` modules.
+
+## Pull Request Checklist
+
+- [ ] Tests pass: `cargo test`
+- [ ] No warnings: `cargo clippy -- -D warnings`
+- [ ] Formatted: `cargo fmt --check`
+- [ ] No tutorial comments
+- [ ] Commit message follows convention

Dockerfile

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+FROM rust:1.75-bookworm as builder
+
+WORKDIR /app
+COPY Cargo.toml Cargo.lock ./
+COPY crates ./crates
+
+RUN cargo build --release
+
+FROM debian:bookworm-slim
+
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends ca-certificates && \
+    rm -rf /var/lib/apt/lists/*
+
+COPY --from=builder /app/target/release/zgrok /usr/local/bin/
+COPY --from=builder /app/target/release/zgrok-edge /usr/local/bin/
+
+EXPOSE 443 80
+
+ENTRYPOINT ["zgrok-edge"]