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

justfile

@@ -0,0 +1,60 @@
+# Default: run all checks
+default: build
+
+# Run all checks (fmt, clippy, test)
+check: fmt-check clippy test audit
+
+# Format code
+fmt:
+    cargo fmt
+
+# Check formatting without changing files
+fmt-check:
+    cargo fmt --check
+
+# Lint with clippy (pedantic + nursery)
+clippy:
+    cargo clippy --all-targets -- -D warnings
+
+# Build release binary
+build:
+    cargo build --release
+
+# Generate docs
+doc:
+    cargo doc --no-deps --open
+
+# Run the bridge (TUI mode)
+run *ARGS:
+    cargo run --release -- {{ARGS}}
+
+# Run in headless mode
+run-headless *ARGS:
+    cargo run --release -- --log-only {{ARGS}}
+
+# Run the config wizard
+config:
+    cargo run --release -- config
+
+# Security + license audit
+audit:
+    cargo deny check
+
+# Run all tests
+test: test-unit test-fuzz test-mutants
+
+# Normal unit tests
+test-unit:
+    cargo nextest run
+
+# Mutation testing
+test-mutants *ARGS:
+    cargo mutants {{ARGS}}
+
+# Fuzz a target (requires nightly)
+test-fuzz TARGET="fuzz_gossip_frame_decode" DURATION="60":
+    cargo +nightly fuzz run {{TARGET}} -- -max_total_time={{DURATION}}
+
+# Clean build artifacts
+clean:
+    cargo clean