dsh-teammate-model-picker: Switch models individually for DSH teammate sessions.

In DSH's teammate sessions, the Lead's model is written into the durable descriptor during dispatch, and the default model is no longer re-parsed afterwards. Once the quota is exhausted, the official model switching capability explicitly rejects subagent sessions, leaving teammates in a stuck state. This plugin installs a bundle; the Host side stores each teammate's model override as `Config(overrides)`. Upon `agent/created`, it implements a waterfall override to the final routing equivalent to the official `installModelSelection`. The Client side registers a model/inference level selector on the right side of the composer toolbar, which renders exclusively in teammate sessions. This solution does not modify the official package, introduce new session event types, require intervention when no override is present, or alter the global default model. It is available via npm as `@wufeng0105/dsh-teammate-model-picker`, version 0.3.2. The documentation includes problem analysis, implementation details, installation commands, typical usage, and offline and real machine verification commands, as well as known limitations such as seat assignment, style copying, lack of whitelist support, and unconnected agent tools.