fix(cli): make /new, /reset, and /clear start real fresh sessions

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.

hermes_cli/commands.py

@@ -16,9 +16,9 @@ from prompt_toolkit.completion import Completer, Completion
 # Commands organized by category for better help display
 COMMANDS_BY_CATEGORY = {
     "Session": {
-        "/new": "Start a new conversation (reset history)",
-        "/reset": "Reset conversation only (keep screen)",
-        "/clear": "Clear screen and reset conversation (fresh start)",
+        "/new": "Start a new session (fresh session ID + history)",
+        "/reset": "Start a new session (alias for /new)",
+        "/clear": "Clear screen and start a new session",
         "/history": "Show conversation history",
         "/save": "Save the current conversation",
         "/retry": "Retry the last message (resend to agent)",