feat(sessions): a dsh session shows its route config's model while its screen names none

displayModel gains a `config` source, ranked below any report from the running
CLI and above the launch model: custom endpoint, then statusline or screen,
then config, then launch, then nothing. The screen still wins whenever it
names a model, since that is what the running TUI uses.

- Registry data: capabilities.modelDetect gains `configResolver`, a NAMED
  reader (src/model-config-resolvers.ts), like a launcher profile; dsh names
  'deepseek-route' (the reader from the previous commit). `screenLine` becomes
  optional; the schema refuses a modelDetect naming nothing, an unknown
  reader, or screenLines without a screenLine.
- Session: the reader runs from _withPaneLifecycle's finally, so at every pane
  start, attach and relaunch, with the session's own launch config
  (legacyConfigForMode) and env (its clamped overrides, then the server's), so
  a per-session DSH_HOME is the home read. Async; a read that lands after a
  newer one or after the session stopped is dropped; a remote or docker
  session reads nothing locally. A change emits displayModelChanged
  (broadcast and persist). Not restored after a restart: the next attach
  reads it again, and a restored screen value outranks it.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/config/cli-registry/stock.ts

@@ -1243,6 +1243,9 @@ const DEEPSEEK: CliEntry = {
     modelDetect: {
       screenLine: String.raw`╰─+╯\n ?([A-Za-z0-9][\w.:/@+-]{0,79})(?= · |\n|$)`,
       screenLines: 3,
+      // With the status bar's model field off (or before it paints), the route the
+      // session's profile pins, read the way dsh-TUI resolves it: src/deepseek-route-config.ts.
+      configResolver: 'deepseek-route',
     },
     // Only-if-sent, like codex/antigravity/grok: an ABSENT permissionMode means the
     // launcher's own default, `workspace-write`, which already asks. Clamping to