fix: reset module state on session_start to fix /new (daemon reconnect + fresh name) - #20

Problem

Typing /new in a pi session causes two issues:

1. The agent-identity status gets permanently stuck at 🟡 <name> (connecting to daemon...)
2. The new session reuses the old agent name instead of generating a fresh one

Root cause

Both stem from module-level variables that persist when /new reuses the same pi process and extension module:

1. shuttingDown — set to true during session_shutdown but never reset. connectToDaemon() returns immediately at its guard clause.
2. agentName — retains the previous session's name. After the restore loop finds nothing in the new (empty) session file, if (!agentName) is false, so generateName() is never called.

Fix

Reset both at the top of session_start:

shuttingDown = false;
agentName = "";

Tested

• ✅ All 10 existing tests pass
• ✅ Manual tmux test: after /new, status transitions 🟡 connecting → 🟢 connected
• ✅ Manual tmux test: after /new, agent name changes (e.g. shadow-raven-24 → silver-quail-9)
• ✅ Daemon log confirms clean reconnect: old connection ghosted → immediately replaced by new registration

— gentle-newt-20