fix(tui): tolerate malformed terminal input bytes

[HamsteRider-m]

What

• Patch tui_v2 startup to make Textual's POSIX input decoder replace malformed UTF-8 bytes instead of crashing the input thread.
• Keep the change local to frontends/tuiapp_v2.py and avoid touching site-packages.

Why

tui_v2 could appear to lose sessions when the Textual input thread crashed on a malformed terminal byte (UnicodeDecodeError). The sessions were still present, but the UI could die before recovery/listing stayed usable.

Testing

• /Users/maygo/Projects/GenericAgent/.venv/bin/python -m py_compile frontends/tuiapp_v2.py
• Imported tuiapp_v2 with sys.path[:0]=['frontends', '.']
• Synthetic decoder check: invalid UTF-8 byte b'\\xb5' decodes to U+FFFD; non-UTF-8 decoder path remains unchanged
• Existing session discovery check: continue_cmd.list_sessions() returned 802 sessions in the local environment