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/035-channels-pure-channel-multiplexing.md

@@ -80,7 +80,7 @@ on the `BiStream` the channels layer gives them.
   doesn't carry control. The "control isn't actually bidirectional" flaw
   is fixed at the TTY layer, not the channels layer.
 - **Recursive composition is literal.** A channel with ALPN
-  `alknet/channels` runs another channels demux on its `BiStream`. The
+  `alk/channels` runs another channels demux on its `BiStream`. The
   outer layer strips its 8-byte header; the inner layer parses its own
   8-byte header from the payload. Each level is the same shape —
   `BiStream → accept_bi → N BiStreams`.
@@ -122,7 +122,7 @@ 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.
@@ -193,7 +193,7 @@ handler's framing, carried transparently.
 
 | 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` (16 MiB, matching TTY's cap — ADR-052 §5). |
 
 The `stream_type` byte is **removed** from the channels header. The
@@ -231,8 +231,8 @@ ADR-077's two-mode TTY design (direct vs inside-channels) is reversed.
 TTY's 5-byte format (`[stream_type:u8][length:u32][payload]`, ADR-052) is
 TTY's internal format, used in *both* direct mode and inside-channels
 mode. The two modes differ only in *where the `BiStream` comes from*
-(a top-level `alknet/tty` connection vs a `channel/open` with ALPN
-`alknet/tty`), not in *how TTY parses it*. The same `wire.rs` code runs
+(a top-level `alk/tty` connection vs a `channel/open` with ALPN
+`alk/tty`), not in *how TTY parses it*. The same `wire.rs` code runs
 in both modes.
 
 When TTY is inside channels, the channels layer strips its 8-byte header
@@ -272,7 +272,7 @@ TTY inside channels:
 ```
 
 The composition is uniform — the same shape at every level. A
-`alknet/channels`-inside-`alknet/channels` recursive composition is the
+`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.
 
@@ -284,7 +284,7 @@ outer layer stripping its 8-byte header, the inner layer parsing its own
   transport leaf; this ADR settles the multiplexing layer above it).
 - **`ProtocolHandler` trait shape** (ADR-002) — unchanged. Handlers
   receive a `Connection` and call `accept_bi()`.
-- **Channel 0 pre-negotiated as `alknet/call`** (ADR-036) — unchanged.
+- **Channel 0 pre-negotiated as `alk/call`** (ADR-036) — unchanged.
   Channel 0's chunks have `channel_id = 0` in the 8-byte header. The call
   protocol's `EventEnvelope` framing is the payload; the channels layer
   carries it transparently.
@@ -345,7 +345,7 @@ outer layer stripping its 8-byte header, the inner layer parsing its own
   byte it doesn't use; no handler needs a second accessor
   (`into_sub_streams`) to reach its sub-streams. The channels layer's
   API surface is `accept_bi -> BiStream`, period.
-- **Recursive composition is literal.** A `alknet/channels` channel runs
+- **Recursive composition is literal.** A `alk/channels` channel runs
   another channels demux on its `BiStream`. The outer layer strips its
   8-byte header; the inner layer parses its own 8-byte header from the
   payload. Same code, same shape, each level. This is a property, not a
@@ -452,7 +452,7 @@ breaking the wire format or the handler contract.
   public stream constructor)
 - ADR-008: `BidiStreamSource` trait (the extension point
   `ChannelBidiStreamSource` implements; `accept_bi` yields `BiStream`)
-- ADR-036: channel 0 pre-negotiated `alknet/call` (unchanged — channel 0's
+- ADR-036: channel 0 pre-negotiated `alk/call` (unchanged — channel 0's
   chunks have `channel_id = 0` in the 8-byte header; the call protocol's
   framing is the payload)
 - ADR-037: channel lifecycle operations (amended — `stream_types` field