feat: add TUI session orchestrator

Add a first-class active-session orchestrator for the Ink TUI:

- list, activate, close, and launch live process-local TUI sessions
- hydrate committed and in-flight output when switching sessions
- dispatch a new prompt session from the +new row with session-scoped model picks
- expose a clickable live-session count in the status chrome
- preserve stable row order while initially focusing the current session
- support mouse hit-testing for floating orchestrator overlays
- add backend and frontend regression coverage for the lifecycle and UI helpers

website/docs/developer-guide/programmatic-integration.md

@@ -41,7 +41,8 @@ hermes acp --bootstrap      # print install snippet for an ACP-capable IDE
 
 ```
 prompt.submit           prompt.background       session.steer
-session.create          session.list            session.interrupt
+session.create          session.list            session.active_list
+session.activate        session.close           session.interrupt
 session.history         session.compress        session.branch
 session.title           session.usage           session.status
 clarify.respond         sudo.respond            secret.respond
@@ -52,6 +53,8 @@ delegation.status       subagent.interrupt      spawn_tree.save / list / load
 terminal.resize         clipboard.paste         image.attach
 ```
 
+`session.active_list`, `session.activate`, and `session.close` are the process-local live-session controls used by the TUI session switcher. Use `session.list` / `/resume` for saved transcript discovery; use the active-session methods only for sessions that are currently open in the TUI gateway process.
+
 ### Events streamed back
 
 `message.delta`, `message.complete`, `tool.start`, `tool.progress`, `tool.complete`, `approval.request`, `clarify.request`, `sudo.request`, `secret.request`, `gateway.ready`, plus session lifecycle and error events.