fix(tui): move all store writes out of Update into tea.Cmds

Deletes, pause toggles, maintenance end, theme/collapse prefs, and all
four form submits wrote to the store synchronously on the UI goroutine;
with busy_timeout=5000 a contended DB froze input for up to 5s.

Writes now run through a writeCmd helper returning writeDoneMsg. The
in-memory engine/model mutations stay in Update so rows react
instantly; the reply logs failures and reloads tab data, so the UI
converges on what was actually written. Closures capture snapshotted
values only — never the model.

internal/tui/messages.go

@@ -54,3 +54,11 @@ type slaDataMsg struct {
 	periodIdx int
 	changes   []models.StateChange
 }
+
+// writeDoneMsg reports a store mutation that ran off the UI goroutine. op
+// names the action for the error log; the handler reloads tab data so the UI
+// converges on what was actually written.
+type writeDoneMsg struct {
+	op  string
+	err error
+}