Move the interactive session — username read, vim-style key dispatcher,
main poll/redraw/keepalive/idle-timeout loop, the @mention bell, and
the tear-down path — out of ssh_server.c into a dedicated module.
New API (include/input.h):
- input_init() -- read TNT_IDLE_TIMEOUT once at startup
- input_run_session(client_t*) -- run the interactive session for an
already-bootstrapped client_t,
including exec_dispatch() short-circuit
when client->exec_command is set
- notify_mentions(content, sender) -- moved from ssh_server.h since
the INSERT-mode send path lives here
too
Renamed: client_handle_session(void *arg) -> input_run_session(client_t *).
The old void* signature was a fossil from when this was a pthread entry;
bootstrap.c calls it synchronously inside its own detached thread.
bootstrap_run() now ends with `input_run_session(client); return NULL;`.
g_idle_timeout is now private to input.c; ssh_server_init() calls
input_init() instead of reading the env directly.
ssh_server.c shrinks from 1026 to 402 lines (-624) -- now down to just
the accept loop, ssh_server_init / ssh_server_start, host-key setup,
client_t I/O API (send/printf/addref/release), and the post-bootstrap
client_channel_* callbacks. M6 will give those a proper home.
Behaviour is preserved: all moved code is byte-for-byte identical.
