fix(tui): move blocking DB IO out of Update/View into tea.Cmds

The TUI ran database queries on the UI goroutine: handleTick called
refreshData every second, which issued four blocking SQLite queries
(GetAllAlerts/GetAllUsers/GetAllNodes/GetAllMaintenanceWindows) and
swallowed their errors; viewDetailPanel ran GetStateChanges — a DB query
— inside View(), on every render (tick, keypress, mouse). A slow disk
stalled input and animation.

Split refreshData into refreshLive() (in-memory engine copies only —
sites + logs — safe every tick) and loadTabDataCmd(), a tea.Cmd that
loads the four DB-backed tables off the UI goroutine and returns a
tabDataMsg. handleTick now refreshes live state every tick but dispatches
the tab-data load only when older than tabRefreshTTL (5s), so tab-bar
counts stay fresh without a per-second query storm. Errors surface to the
log instead of being dropped, and a transient failure keeps the previous
data rather than blanking the view.

The detail panel's state-change history is loaded once on enter via
loadDetailCmd and cached on the model; viewDetailPanel reads the cache,
so View no longer touches the database. Init kicks an initial load so the
dashboard isn't empty on the first frame, and the bare time.Time tick
message is now a named tickMsg (no cross-message collision). The
test-alert handler's raw goroutine becomes a tea.Cmd.

Adds the package's first Update()-driven tests: tab-data load + apply,
error-keeps-previous-data, detail cache with a store-hit counter proving
View does zero IO across repeated renders, and the handleTick throttle.
Full suite green under -race; golangci-lint clean.

internal/tui/update.go

@@ -15,8 +15,14 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 	switch msg := msg.(type) {
 	case tea.WindowSizeMsg:
 		return m.handleResize(msg)
-	case time.Time:
-		return m.handleTick(msg)
+	case tickMsg:
+		return m.handleTick(time.Time(msg))
+	case tabDataMsg:
+		return m.handleTabData(msg)
+	case detailDataMsg:
+		m.detailChanges = msg.changes
+		m.detailChangesSiteID = msg.siteID
+		return m, nil
 	}
 
 	if m.state == stateConfirmDelete {
@@ -65,11 +71,12 @@ func (m *Model) handleConfirmDelete(msg tea.Msg) (tea.Model, tea.Cmd) {
 			}
 			m.adjustCursor(len(m.users) - 1)
 		}
-		m.refreshData()
+		m.refreshLive()
 		m.state = stateDashboard
 		if m.deleteTab == 5 {
 			m.state = stateUsers
 		}
+		return m, m.loadTabDataCmd()
 	case "n", "N", "esc":
 		m.state = stateDashboard
 		if m.deleteTab == 5 {
@@ -106,9 +113,9 @@ func (m *Model) handleFormMsg(msg tea.Msg) (tea.Model, tea.Cmd) {
 		}
 		if m.huhForm.State == huh.StateCompleted {
 			m.submitForm()
-			m.refreshData()
+			m.refreshLive()
 			m.huhForm = nil
-			return m, nil
+			return m, m.loadTabDataCmd()
 		}
 		return m, formCmd
 	}
@@ -136,11 +143,47 @@ func (m *Model) handleResize(msg tea.WindowSizeMsg) (tea.Model, tea.Cmd) {
 }
 
 func (m *Model) handleTick(t time.Time) (tea.Model, tea.Cmd) {
-	m.refreshData()
+	m.refreshLive()
 	m.tickCount++
 	target := sinApprox(float64(m.tickCount)*0.3)*0.5 + 0.5
 	m.pulsePos, m.pulseVel = m.pulseSpring.Update(m.pulsePos, m.pulseVel, target)
-	return m, tea.Tick(time.Second, func(t time.Time) tea.Msg { return t })
+
+	cmds := []tea.Cmd{tickCmd()}
+	if t.Sub(m.lastTabLoad) > tabRefreshTTL {
+		m.lastTabLoad = t
+		cmds = append(cmds, m.loadTabDataCmd())
+	}
+	return m, tea.Batch(cmds...)
+}
+
+// handleTabData folds an async tab-data load into the model. On error the
+// previous data is kept and the failure logged, so a transient store error
+// never blanks the view.
+func (m *Model) handleTabData(msg tabDataMsg) (tea.Model, tea.Cmd) {
+	if msg.err != nil {
+		m.engine.AddLog("Tab data refresh failed: " + msg.err.Error())
+		return m, nil
+	}
+	m.alerts = msg.alerts
+	if m.isAdmin {
+		m.users = msg.users
+	}
+	m.nodes = msg.nodes
+	m.maintenanceWindows = msg.maint
+	m.clampCursor()
+	return m, nil
+}
+
+// testAlertCmd sends a test notification off the UI goroutine; the outcome
+// surfaces through the engine log (picked up by the next refreshLive).
+func (m *Model) testAlertCmd(id int, name string) tea.Cmd {
+	eng := m.engine
+	return func() tea.Msg {
+		if err := eng.TestAlert(id); err != nil {
+			eng.AddLog(fmt.Sprintf("Test alert failed (%s): %v", name, err))
+		}
+		return nil
+	}
 }
 
 func (m *Model) handleMouse(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
@@ -240,7 +283,7 @@ func (m *Model) handleFilterKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 		m.filterText = ""
 		m.cursor = 0
 		m.tableOffset = 0
-		m.refreshData()
+		m.refreshLive()
 	case "enter":
 		m.filterMode = false
 	case "backspace":
@@ -248,7 +291,7 @@ func (m *Model) handleFilterKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 			m.filterText = m.filterText[:len(m.filterText)-1]
 			m.cursor = 0
 			m.tableOffset = 0
-			m.refreshData()
+			m.refreshLive()
 		}
 	case "ctrl+c":
 		return m, tea.Quit
@@ -257,7 +300,7 @@ func (m *Model) handleFilterKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 			m.filterText += msg.String()
 			m.cursor = 0
 			m.tableOffset = 0
-			m.refreshData()
+			m.refreshLive()
 		}
 	}
 	return m, nil
@@ -459,19 +502,14 @@ func (m *Model) handleDashboardKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 	case "t":
 		if m.currentTab == 1 && len(m.alerts) > 0 {
 			a := m.alerts[m.cursor]
-			go func() {
-				if err := m.engine.TestAlert(a.ID); err != nil {
-					m.engine.AddLog(fmt.Sprintf("Test alert failed (%s): %v", a.Name, err))
-				}
-			}()
-			return m, nil
+			return m, m.testAlertCmd(a.ID, a.Name)
 		}
 	case " ":
 		if m.currentTab == 0 && len(m.sites) > 0 && m.sites[m.cursor].Type == "group" {
 			gid := m.sites[m.cursor].ID
 			m.collapsed[gid] = !m.collapsed[gid]
 			saveCollapsed(m.store, m.collapsed)
-			m.refreshData()
+			m.refreshLive()
 		}
 	case "p":
 		if m.currentTab == 0 && len(m.sites) > 0 {
@@ -479,11 +517,12 @@ func (m *Model) handleDashboardKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 			m.engine.ToggleSitePause(site.ID)
 			site.Paused = !site.Paused
 			_ = m.store.UpdateSitePaused(site.ID, site.Paused)
-			m.refreshData()
+			m.refreshLive()
 		}
 	case "i":
 		if m.currentTab == 0 && len(m.sites) > 0 {
 			m.state = stateDetail
+			return m, m.loadDetailCmd(m.sites[m.cursor].ID)
 		} else if m.currentTab == 1 && len(m.alerts) > 0 {
 			m.state = stateAlertDetail
 		}
@@ -496,7 +535,8 @@ func (m *Model) handleDashboardKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 				if err := m.store.EndMaintenanceWindow(mw.ID); err != nil {
 					m.engine.AddLog("End maintenance failed: " + err.Error())
 				}
-				m.refreshData()
+				m.refreshLive()
+				return m, m.loadTabDataCmd()
 			}
 		}
 	case "T":