refactor(console): route interactive prompts through a themed helper

Adds prompt_user() and uses it for local, remote, and Proton VPN input. Replaces click.prompt on the remote auth path, which ignored the theme and overlapped active Live displays. Remote auth now exits on EOF instead of POSTing an empty answer and spinning the poll loop.

docs/dev/creating-a-service.md

@@ -242,7 +242,7 @@ use `self.request_input(prompt)`, never a bare `input()`. Under `serve` mode
 there is no local terminal, so a bare `input()` would hang the server waiting on
 stdin that never arrives; `request_input` instead relays the prompt to the
 remote client through the attached `InputBridge`. Locally it routes through the
-shared Rich console (`console.input`) so the prompt renders correctly alongside
+shared Rich console (`prompt_user`) so the prompt renders correctly alongside
 progress and log output.
 
 !!! warning "Key token caches by whatever varies per session"

docs/dev/rest-api/remote-sessions.md

@@ -398,7 +398,8 @@ session API and a good template for any client.
 - **Retries.** The download-side HTTP session mounts an adapter with
   `Retry(total=5, backoff_factor=0.2, status_forcelist=[429, 500, 502, 503, 504])`.
 - **Flow.** `authenticate()` → `create` (+ poll `prompt` every 2s up to a 600s
-  deadline, answering `pending_input` prompts) → `get_titles()` → `get_tracks()`
+  deadline, answering `pending_input` prompts; with stdin closed the client logs an
+  error and raises `SystemExit(1)` instead of posting an empty answer) → `get_titles()` → `get_tracks()`
   (merging returned `session_headers`/`session_cookies`, re-parsing `manifests`) →
   license via proxy or `server_cdm` → `close()` (`DELETE`, saving any returned
   `cache`).