feat: add interactive recipient composer

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a03397-4d51-7fd1-8ff2-946eb22ea2bc

README.md

@@ -77,17 +77,27 @@ The spelling without the trailing colon is equivalent:
 @audit-core please review the auth boundary
 ```
 
-After receiving a message, use the bare `@` command to answer its sender:
+Run bare `@` to open the inline composer. It shows the latest sender as the
+recipient, and ordinary prose is read directly rather than parsed by the shell:
 
-```bash
-@ Thanks, I will take a look.
+```text
+$ @
+@audit-core: What's up?
 ```
 
-Bare `@` selects the sender of the latest durable inbound message for the
-current repository, including an already acknowledged message. Self-addressed
-messages are ignored. If this window has no prior counterparty, the command
-reports an error and queues nothing. The explicit equivalent is `tamq reply
-MESSAGE...`.
+Press Tab to cycle through the other repository windows while preserving the
+draft, Enter to send, or Ctrl-C to cancel without queuing. The initial recipient
+is the sender of the latest durable inbound message, including an already
+acknowledged message; without history, it is the first peer window.
+Self-addressed messages are ignored.
+
+The one-line fast path remains available, but its text is parsed by the shell
+and therefore follows ordinary shell quoting rules:
+
+```bash
+@ "What's up?"
+tamq reply "What's up?"
+```
 
 These are tamq-owned executable commands beside the installed `tamq` command,
 not shell-specific aliases. Set `TAMQ_COMMAND_DIR` before startup to select a