release prep: opt-in web UI, make uninstall, fix stale kernel-catalog docs

- WebListenAddr default is now "" (empty). The experimental web UI was
  running on 127.0.0.1:7777 by default, which surprises users who never
  opted in. Users who want it set `web_listen_addr = "127.0.0.1:7777"`
  in config.toml.
- `make uninstall` stops the daemon (if any) and removes the installed
  binaries. Preserves user data on disk but prints the paths so `rm -rf`
  can follow for a full purge. Documented in README next to install.
- docs/kernel-catalog.md: replace the `void-6.12` and `alpine-3.23`
  examples (never published) with `generic-6.12` (the only cataloged
  kernel today). Updates the versioning-convention example too.

internal/config/config.go

@@ -44,8 +44,10 @@ type fileSyncEntryFile struct {
 
 func Load(layout paths.Layout) (model.DaemonConfig, error) {
 	cfg := model.DaemonConfig{
-		LogLevel:            "info",
-		WebListenAddr:       "127.0.0.1:7777",
+		LogLevel: "info",
+		// Experimental web UI is opt-in: users set web_listen_addr in
+		// config.toml (e.g. "127.0.0.1:7777") to enable it.
+		WebListenAddr:       "",
 		AutoStopStaleAfter:  0,
 		StatsPollInterval:   model.DefaultStatsPollInterval,
 		MetricsPollInterval: model.DefaultMetricsPollInterval,