Follow-up to PR #2101 (InB4DevOps). Adds three missing context compressor
resets in reset_session_state():
- compression_count (displayed in status bar)
- last_total_tokens
- _context_probed (stale context-error flag)
Also fixes the test_cli_new_session.py prompt_toolkit mock (missing
auto_suggest stub) and adds a regression test for #2099 that verifies
all token counters and compressor state are zeroed on /new.
Create a new session DB row when starting fresh from the CLI, reset the
agent DB flush cursor and todo state, and update session timing/session ID
bookkeeping so follow-up logging stays correct.
Also update slash-command descriptions and add regression tests for /new,
/reset, and /clear.
Supersedes PR #899.
Closes#641.