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

.github/workflows/ci.yml

@@ -0,0 +1,44 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Clone donglora (sibling dependency)
+        uses: actions/checkout@v4
+        with:
+          repository: swaits/donglora
+          path: ../donglora
+
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.94.1"
+          components: rustfmt, clippy
+
+      - uses: Swatinem/rust-cache@v2
+
+      - name: Format check
+        run: cargo fmt --check
+
+      - name: Clippy
+        run: cargo clippy --all-targets -- -D warnings
+
+      - name: Test
+        run: cargo test
+
+      - name: Install cargo-deny
+        run: cargo install cargo-deny --locked
+
+      - name: Audit (advisories + licenses)
+        run: cargo deny check