feat(desktop): stop the daemon when you quit the app (#2454)

Quitting the desktop app now shuts down the daemon it started, so
"restart the app" is a complete reset users can act on without first
learning what a daemon is. The old default kept it alive; the toggle
under Settings > Host still opts back in.

Existing installs already persisted `keepRunningAfterQuit: true` from
the old default, so a new default alone would only reach fresh installs.
A one-time migration resets it, and an explicit toggle afterwards
persists the migration flag and is never overridden again.

Only a desktop-managed daemon is stopped — one started with
`paseo daemon start` is left alone.

docs/architecture.md

@@ -382,5 +382,5 @@ $PASEO_HOME/
 ## Deployment models
 
 1. **Local daemon** (default): `paseo daemon start` on `127.0.0.1:6767`
-2. **Managed desktop**: Electron app spawns daemon as subprocess
+2. **Managed desktop**: Electron app spawns daemon as subprocess, and stops it again on quit so that "restart the app" is a complete reset. Settings > Host > "Keep daemon running after quit" opts out. Only a daemon the desktop started is stopped — a daemon you started yourself with `paseo daemon start` is left alone (`paseo.pid` records `desktopManaged`).
 3. **Remote + relay**: Daemon behind firewall, relay bridges with E2E encryption

docs/product.md

@@ -43,7 +43,8 @@ This architecture means:
 
 - The daemon can run on any machine: laptop, VM, remote server
 - Multiple clients can connect simultaneously
-- Agents keep running when you close the app
+- Agents keep running when a client disconnects — the daemon owns them, not the client
+- Quitting the desktop app stops the daemon it started, so "restart the app" is a real fix; a daemon you run yourself is unaffected
 
 ## Target user