Add fresh default sessions and terminal status handling

SPEC.md

@@ -321,14 +321,9 @@ Reliability:
 Named sessions:
 
 ```bash
-dosh                       # attach default
-dosh attach                # attach default
-dosh attach work
-dosh attach work --view-only
-dosh new work
-dosh list
-dosh list-clients [session]
-dosh kill work
+dosh host                  # open a fresh generated session
+dosh --session work host   # attach/create named persistent session
+dosh --session work --view-only host
 ```
 
 Session behavior:
@@ -336,6 +331,8 @@ Session behavior:
 - One PTY per session.
 - Sessions persist until killed or server exits.
 - If a session has zero clients, the PTY keeps running.
+- Plain client attaches use generated session names by default.
+- `--session <name>` intentionally reuses or shares a persistent session.
 - Configured sessions are prewarmed at daemon startup.
 - If a requested session does not exist:
   - `attach` creates it only when `create_on_attach = true`.
@@ -457,7 +454,7 @@ server = "user@example.com"
 ssh_auth_command = "~/.local/bin/dosh-auth"
 # ssh_port = 22
 dosh_port = 50000
-default_session = "default"
+default_session = "new"
 reconnect_timeout_secs = 5
 view_only = false
 cache_attach_tickets = true