feat(doctor): add env-vars check, remove redundant gtroot check

Adds a new `gt doctor` check that verifies tmux session environment
variables match expected values from `config.RoleEnvVars()`.

- Checks all Gas Town sessions (gt-*, hq-*)
- Compares actual tmux env vars against expected for each role
- Reports mismatches with guidance to restart sessions
- Treats no sessions as success (valid when Gas Town is down)
- Skips deacon (doesn't use standard env vars)

Also:
- Adds `tmux.GetAllEnvironment()` to retrieve all session env vars
- Removes redundant gtroot_check (env-vars check covers GT_ROOT)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/doctor.go

@@ -133,7 +133,6 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	d.Register(doctor.NewRoutesCheck())
 	d.Register(doctor.NewOrphanSessionCheck())
 	d.Register(doctor.NewOrphanProcessCheck())
-	d.Register(doctor.NewGTRootCheck())
 	d.Register(doctor.NewWispGCCheck())
 	d.Register(doctor.NewBranchCheck())
 	d.Register(doctor.NewBeadsSyncOrphanCheck())
@@ -142,6 +141,7 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	d.Register(doctor.NewLinkedPaneCheck())
 	d.Register(doctor.NewThemeCheck())
 	d.Register(doctor.NewCrashReportCheck())
+	d.Register(doctor.NewEnvVarsCheck())
 
 	// Patrol system checks
 	d.Register(doctor.NewPatrolMoleculesExistCheck())