feat(serve): detach from an attached serve session with Ctrl-D (#85)

* feat(serve): detach from an attached serve session with Ctrl-D

`rocm serve --verbose`/`--foreground` ran the engine in-process, so the
only way out was Ctrl-C, which killed the model. The attached path now
spawns the same detached managed child the background path uses and tails
its log, so the server outlives the session: Ctrl-D detaches and leaves it
running (manage it later with `rocm services`), while Ctrl-C stops it.

Split the engine spawn out of start_managed_service so the attached path
streams startup logs live instead of blocking on the readiness wait.

Signed-off-by: Eugene Volen <Eugene.Volen@amd.com>

* fix(serve): supervise and harden the attached detach path

Address review on the attached serve path:

- Ensure the supervisor daemon is running after spawning the attached
  child, so a Ctrl-D-detached server gets the same health-check,
  auto-recovery, record reconciliation, and dashboard metrics a
  background-managed server gets.
- Enter raw mode before spawning the key reader thread, closing a window
  where a terminal Ctrl-C would kill the CLI with no detach/stop message.
- Discover AppPaths once and thread it into spawn_managed_engine_child
  instead of rediscovering it per call.

Signed-off-by: Eugene Volen <Eugene.Volen@amd.com>

---------

Signed-off-by: Eugene Volen <Eugene.Volen@amd.com>

Author: volen-silo

README.md

@@ -190,10 +190,13 @@ quick smoke test (time to first token and approximate tokens/sec). Control
 returns to your shell with the server still running; manage it later with `rocm
 services` (below).
 
-`--verbose` (or `--foreground`) instead attaches the server to the current
+`--verbose` (or `--foreground`) instead attaches to the server in the current
 terminal and streams every engine log line — use it to debug a startup problem.
-`--managed` is the explicit form of the default background behavior.
-`--no-smoke-test` skips the post-startup inference probe.
+The server still runs as a managed background process, so while streaming you can
+press **Ctrl-D to detach** — the log stream stops, your shell comes back, and the
+server keeps running (manage it afterward with `rocm services`). Press **Ctrl-C**
+to stop the server instead. `--managed` is the explicit form of the default
+background behavior. `--no-smoke-test` skips the post-startup inference probe.
 
 Use full HuggingFace model IDs (e.g., `Qwen/Qwen2.5-1.5B-Instruct`) for
 reliable cross-engine compatibility. Short aliases from `rocm model` may not