controller v0.67.1: gate only acts on external drives under /mnt/felhom-drives/

Fix caught live: planDriveGates falsely marked the internal SSD path
/mnt/sys_drive/felhom-data disconnected (agent never reports it), which would
block starting SSD-resident apps. Gate now skips non-/mnt/felhom-drives/ paths.
Regression case added. No apps were stopped (none depended on the SSD path).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

controller/internal/web/intermediary.go

@@ -105,6 +105,14 @@ func planDriveGates(paths []settings.StoragePath, disks []agentapi.DiskInfo) []g
 		if sp.Decommissioned {
 			continue
 		}
+		// ONLY gate EXTERNAL drives — those registered under the stable parent /mnt/felhom-drives/<name>.
+		// Internal SSD / system paths (e.g. /mnt/sys_drive/felhom-data) are always-present locals the agent
+		// never reports as drives; gating them on "absence" would falsely stop/block their apps. (Legacy
+		// raw /mnt/<name> external paths are present via the agent's MountPath during the transition and get
+		// repointed under the parent by the migration.)
+		if !strings.HasPrefix(sp.Path, StableParentDir+"/") {
+			continue
+		}
 		switch {
 		case !present[sp.Path] && !sp.Disconnected:
 			actions = append(actions, gateAction{Path: sp.Path, Stop: true})