Add edit/delete history, named sessions, scroll fix, systemd service

- Edit/delete individual messages from session context with inline editing
  (Ctrl+Enter saves, Escape cancels); changes sync to backend via PUT /history
- PUT /history/{session_id} endpoint to replace full message list
- Named sessions: readable slugs (e.g. quiet-spring) instead of UUID fragments
- Scroll no longer snaps to bottom when user has scrolled up to read history
- cortex.service: systemd unit for auto-start and restart-on-failure

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/cortex.service

@@ -0,0 +1,20 @@
+[Unit]
+Description=Cortex / Inara LLM Gateway
+After=network.target
+
+[Service]
+Type=simple
+User=scott
+WorkingDirectory=/home/scott/agents_sync/projects/Cortex_and_Inara_dev/cortex
+ExecStart=/home/scott/agents_sync/projects/Cortex_and_Inara_dev/cortex/.venv/bin/uvicorn main:app --host 0.0.0.0 --port 8000
+Restart=on-failure
+RestartSec=5
+
+# Pass through the user's environment so API keys in ~/.env or shell env are available
+EnvironmentFile=-/home/scott/agents_sync/projects/Cortex_and_Inara_dev/cortex/.env
+
+# Give LLM subprocesses time to finish before force-kill
+TimeoutStopSec=15
+
+[Install]
+WantedBy=multi-user.target