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

deny.toml

@@ -0,0 +1,41 @@
+# cargo-deny configuration (v0.19+)
+# Run with: cargo deny check
+
+[licenses]
+version = 2
+
+# Permissive licenses only. No copyleft.
+allow = [
+    "MIT",
+    "MIT-0",
+    "Apache-2.0",
+    "BSD-1-Clause",
+    "BSD-2-Clause",
+    "BSD-3-Clause",
+    "BSL-1.0",
+    "ISC",
+    "Zlib",
+    "Unlicense",
+    "CC0-1.0",
+    "CDLA-Permissive-2.0",
+    "Unicode-3.0",
+    "MPL-2.0",
+]
+
+[advisories]
+# Unmaintained transitive deps from upstream (iroh dep tree) — not actionable by us.
+ignore = [
+    "RUSTSEC-2023-0089", # atomic-polyfill: unmaintained (transitive via iroh)
+    "RUSTSEC-2024-0436", # paste: unmaintained (transitive via iroh)
+]
+
+[bans]
+multiple-versions = "warn"
+wildcards = "warn"
+
+[sources]
+unknown-registry = "deny"
+unknown-git = "warn"
+allow-git = [
+    "https://github.com/swaits/donglora",
+]