feat(cli): set terminal tab title from session title via OSC 0

[rumbin]

Summary

When running multiple Hermes sessions in separate terminal tabs (e.g. Ghostty, iTerm2, Kitty), every tab shows the generic title Hermes. This PR makes each tab reflect the actual session title, so users can distinguish sessions at a glance.

What changes

agent/title_generator.py

• Added an optional on_title callback parameter to auto_title_session and maybe_auto_title
• After a title is successfully saved to the DB, the callback is invoked with the new title string
• The callback is forwarded through the background thread kwargs so the thread result reaches the CLI

cli.py

• Added HermesCLI._set_terminal_title(title) — emits the standard OSC 0 escape sequence ESC]0;Hermes: <title>BEL to stdout, which all modern terminals interpret as a tab/window title update
• Wired it into all 5 title-setting paths:
  1. Auto-title after first exchange — passed as on_title callback to maybe_auto_title so the background thread updates the tab once the LLM-generated title is ready
  2. /title command — immediately updates the tab after saving a manually set title
  3. Pending title flush — updates the tab when a /title set before the first message is finally committed to the DB on session creation
  4. /resume command — sets the tab title when switching to an existing titled session mid-conversation
  5. Startup --continue resume — fetches and sets the tab title immediately on launch when loading an existing session

Behaviour

• New session: tab shows Hermes → switches to Hermes: <generated title> a few seconds after the first exchange
• hermes -c "my project": tab shows Hermes: my project immediately on startup
• /title My Project: tab updates instantly
• All OSC sequences go to sys.stdout directly — same approach as the existing _write_osc52_clipboard helper

Compatibility

OSC 0 is supported by virtually all modern terminal emulators (Ghostty, iTerm2, Kitty, GNOME Terminal, Windows Terminal, WezTerm, Alacritty, xterm). There is no visible side-effect in terminals that don't support it (the sequence is silently ignored).

[alt-glitch]

Related to #10013 (prior attempt at OSC terminal tab titles) and #17148 (JetBrains terminal title request). May supersede #10013.

[alt-glitch]

Related to #10013 and #17148.

[rumbin]

Thanks for the pointers @alt-glitch. After reviewing #10013, I can see tsemana's implementation is considerably more complete — dedicated module, persona-aware title format, sanitisation/injection protection, TTY guards, ACP no-op, and 16 unit tests. Our PR covers the same ground but less thoroughly. Closing in favour of #10013. Hopefully that one lands soon!