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/channels-wire.md

@@ -5,7 +5,7 @@ last_updated: 2026-07-18
 
 # channels-wire.md — The 8-Byte Chunk Format
 
-The wire format for `alknet/channels`: an 8-byte chunk header that
+The wire format for `alk/channels`: an 8-byte chunk header that
 multiplexes N logical channels over a single ordered, reliable
 bidirectional transport stream. ADR-034 (amended by ADR-035) is the
 decision; this doc specifies the format and the wire-level invariants.
@@ -23,7 +23,7 @@ multiplexing on the `BiStream` the channels layer gives it.
 
 | field | offset | width | meaning |
 |-------|--------|-------|---------|
-| `channel_id` | 0 | 4 (BE) | The logical channel this chunk belongs to. Channel 0 is pre-negotiated as `alknet/call` (ADR-036). Channels 1..N are opened dynamically via `channel/open` (ADR-037). |
+| `channel_id` | 0 | 4 (BE) | The logical channel this chunk belongs to. Channel 0 is pre-negotiated as `alk/call` (ADR-036). Channels 1..N are opened dynamically via `channel/open` (ADR-037). |
 | `length` | 4 | 4 (BE) | The payload length in bytes. 0 = EOF sentinel. Max `MAX_CHUNK_LEN`. |
 
 The payload is opaque to the channels layer. The handler parses its own
@@ -70,10 +70,10 @@ stream — the demux drops the chunk and continues. The header is always
 exactly 8 bytes, so the demux can always resync by reading the next
 8-byte header.
 
-## Channel 0 — pre-negotiated `alknet/call`
+## Channel 0 — pre-negotiated `alk/call`
 
 Channel 0 is not a special "control plane" with its own framing. It is
-`alknet/call` pre-negotiated (ADR-036): both sides know `channel_id = 0`
+`alk/call` pre-negotiated (ADR-036): both sides know `channel_id = 0`
 is routed to the `CallAdapter` without an explicit `channel/open`
 exchange.
 
@@ -230,7 +230,7 @@ a `channel_id` was stripped before it saw the bytes.
 
 The composition is uniform — the same shape at every level. This is SSH's
 model (layered headers, each layer strips its own at its boundary),
-applied to channels. A `alknet/channels`-inside-`alknet/channels`
+applied to channels. A `alk/channels`-inside-`alk/channels`
 recursive composition is the outer layer stripping its 8-byte header, the
 inner layer parsing its own 8-byte header from the payload — same code,
 same shape, each level.