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

docs/architecture/decisions/039-channelsadapter-and-channelmanager.md

@@ -30,7 +30,7 @@ The channels crate has two internal components, split by responsibility
 Connection Internals):
 
 1. **`ChannelsAdapter`** — implements `ProtocolHandler` for
-   `alknet/channels`. Its `handle()` receives one `Connection` (the
+   `alk/channels`. Its `handle()` receives one `Connection` (the
    transport), reads 9-byte chunk headers, and routes each chunk. It is the
    read/demux half.
 
@@ -53,12 +53,12 @@ contracts.
 ```rust
 #[async_trait]
 impl ProtocolHandler for ChannelsAdapter {
-    fn alpn(&self) -> &'static [u8] { b"alknet/channels" }
+    fn alpn(&self) -> &'static [u8] { b"alk/channels" }
 
     async fn handle(&self, connection: Connection, auth: &AuthContext)
         -> Result<(), HandlerError>
     {
-        // 1. Channel 0 is pre-negotiated as alknet/call (ADR-036).
+        // 1. Channel 0 is pre-negotiated as alk/call (ADR-036).
         //    The first bidi stream the transport yields is channel 0.
         let (send, recv) = connection.accept_bi().await?;
         self.manager.preinstall_channel_0(send, recv, auth).await?;
@@ -79,7 +79,7 @@ The `preinstall_channel_0` step constructs the reassembly buffers for
 `channel_id = 0` using stream_types [0, 1] (ADR-036), wraps them as a
 `Connection` (via `Connection::from_source` with a `ChannelBidiStreamSource`
 — ADR-038), and hands that `Connection` to the `CallAdapter` — exactly as if
-`alknet/call` had been the top-level ALPN. The `CallAdapter` is looked up in
+`alk/call` had been the top-level ALPN. The `CallAdapter` is looked up in
 the same `HandlerRegistry` as every other ALPN.
 
 `run_demux_loop` continues accepting bidi streams from the transport. For