feat: rename ALPN prefix from alknet/ to alk/ (v0.1.1)

- CHANNELS_ALPN: b"alknet/channels" → b"alk/channels"
- CallAdapter::alpn(): b"alknet/call" → b"alk/call"
- derive_alpn_from_op_name: alknet/ prefix → alk/ prefix
- All ALPN string literals in src/ and docs/ updated
- ADR-004 amended with prefix rename rationale
- AGENTS.md, README.md updated
- Version bumped to 0.1.1

Review: docs/reviews/003-alpn-prefix-rename.md

Verification:
- cargo test: 542 passed, 0 failed
- cargo clippy --all-targets -- -D warnings: clean
- cargo fmt --check: clean
- cargo doc --no-deps: clean

src/channels/wire.rs

@@ -29,7 +29,7 @@ pub const CHUNK_HEADER_LEN: usize = 8;
 /// so the demux can always resync by reading the next 8-byte header.
 pub const MAX_CHUNK_LEN: u32 = 16 * 1024 * 1024;
 
-/// A chunk channel ID of 0 is pre-negotiated as `alknet/call` (ADR-036).
+/// A chunk channel ID of 0 is pre-negotiated as `alk/call` (ADR-036).
 /// Both sides know `channel_id = 0` is routed to the `CallAdapter`
 /// without an explicit open op exchange.
 pub const CHANNEL_ID_ZERO: u32 = 0;