chore: prepare 0.1.0 for crates.io publish

- Cargo.toml: add documentation and readme fields; expand the exclude
  list so deny.toml, justfile, mise.toml, .github, .jj, fuzz, and any
  cargo-mutants output never ship in the published tarball.
- README: badges, install snippet for both feature shapes, testing
  matrix.
- CHANGELOG.md: keep-a-changelog skeleton with a 0.1.0 entry.
- Revert framing.rs let-chain back to nested if-let so the published
  MSRV holds at the edition-2024 floor (1.85). Behaviour unchanged.

cargo publish --dry-run packages cleanly.

Cargo.toml

@@ -8,9 +8,20 @@ license = "MIT"
 description = "DongLoRa wire protocol types and COBS framing — shared between firmware and host crates"
 repository = "https://github.com/donglora/protocol"
 homepage = "https://github.com/donglora/protocol"
+documentation = "https://docs.rs/donglora-protocol"
+readme = "README.md"
 keywords = ["lora", "radio", "protocol", "no-std"]
 categories = ["embedded", "no-std", "encoding"]
-exclude = ["fuzz", ".jj"]
+exclude = [
+    ".github",
+    ".jj",
+    "deny.toml",
+    "fuzz",
+    "justfile",
+    "mise.toml",
+    "mutants.out",
+    "mutants.out.old",
+]
 
 [dependencies]
 heapless = "0.9"