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/037-channel-lifecycle-operations.md

@@ -107,7 +107,7 @@ Request (`call.requested` on channel 0):
 {
   "operation": "channel/open",
   "input": {
-    "alpn": "alknet/tty",
+    "alpn": "alk/tty",
     "stream_types": [0, 1, 2, 3, 4],
     "params": { "backend": "docker", "cmd": ["bash"], "container": "abc123" },
     "direction": "initiator-to-responder"
@@ -119,7 +119,7 @@ Request (`call.requested` on channel 0):
 |-------|------|---------|
 | `alpn` | string | The ALPN the channel will carry. The responder looks this up in its `HandlerRegistry`. |
 | `stream_types` | `[u8]` | Which sub-stream types this channel will use. E.g. `[0,1,2,3,4]` for TTY (data in/out/err + control in/out), `[0,1]` for a tunnel, `[0,1]` for channel 0 (call frames). See ADR-034 §stream_type decomposition. |
-| `params` | object | ALPN-specific parameters. For `alknet/tty` this is the `NegotiateRequest`. For `alknet/tunnel` this is the target resource. The channels layer does not interpret `params`. |
+| `params` | object | ALPN-specific parameters. For `alk/tty` this is the `NegotiateRequest`. For `alk/tunnel` this is the target resource. The channels layer does not interpret `params`. |
 | `direction` | string | `initiator-to-responder` or `responder-to-initiator`. See "Direction semantics" below. |
 
 Response (`call.responded`):
@@ -223,12 +223,12 @@ The responder registers a `StreamingHandler` that emits a
   "output": {
     "resources": [
       {
-        "alpn": "alknet/tty",
+        "alpn": "alk/tty",
         "backends": ["docker", "local"],
         "access": { "required_scopes": ["tty:open"] }
       },
       {
-        "alpn": "alknet/tunnel",
+        "alpn": "alk/tunnel",
         "targets": ["container:*", "service:postgres"],
         "access": { "required_scopes_any": ["tunnel:open", "admin"] }
       }
@@ -355,7 +355,7 @@ the underlying one-way commitment.
 - ADR-035: channels pure channel multiplexing (amends this ADR —
   `stream_types` field removed from `channel/open`; `stream_type` field
   removed from `channel/control`; handler owns sub-stream multiplexing)
-- ADR-036: channel 0 is pre-negotiated `alknet/call`
+- ADR-036: channel 0 is pre-negotiated `alk/call`
 - ADR-021: StreamingHandler for subscriptions (the machinery
   `channel/resources/subscribe` uses — implemented and tested)
 - ADR-020: abort cascade (subscription cancellation)