feat: publish-ready overhaul — lints, tests, docs, CI, fuzzing, mutant testing

- Enable clippy pedantic + nursery lints; fix all warnings
- Add config validation (SF, CR, frequency range checks)
- Zeroize passphrase intermediates after key derivation
- Convert to lib+bin crate for fuzz target accessibility
- Replace Vec with VecDeque for O(1) log/bucket rotation
- Add TUI minimum terminal size guard

Testing:
- 145 unit + property tests (was 15)
- 6 proptest groups (frame roundtrip, hash, SNR, air time, peer list, padding)
- 2 cargo-fuzz targets (gossip frame decode, peer list decode)
- cargo-mutants: 0 missed, 241 caught, 54 unviable

Documentation:
- README with prerequisites, quick start, config reference, architecture
- Module-level and item-level rustdoc on all public items
- LICENSE (MIT), rustfmt.toml, .gitignore

Infrastructure:
- GitHub Actions CI (fmt, clippy, test, audit)
- cargo-mutants config (.cargo/mutants.toml)
- justfile for common tasks

src/lib.rs

@@ -0,0 +1,18 @@
+//! Peer-to-peer `LoRa` bridge connecting `DongLoRa` USB dongles across the internet.
+//!
+//! Uses iroh-gossip for swarm-based packet broadcast and mainline DHT for
+//! zero-configuration peer discovery. Nodes sharing a passphrase automatically
+//! discover each other and relay radio packets through a gossip swarm.
+
+pub mod config;
+pub mod gossip;
+pub mod packet;
+pub mod radio;
+pub mod rate_limit;
+pub mod router;
+pub mod setup;
+
+// TUI is public only so its types are visible to the binary; not intended for
+// external consumption.
+#[doc(hidden)]
+pub mod tui;