chore: add golangci-lint config and fix all lint issues

Add .golangci.yml enabling errcheck, staticcheck, govet, gosec,
ineffassign, and unused linters. Fix 66 issues across 16 files:
- Check all unchecked errors (errcheck)
- Use HTTP status constants instead of numeric literals (staticcheck)
- Replace deprecated LineUp/LineDown with ScrollUp/ScrollDown (staticcheck)
- Convert sprintf+write patterns to fmt.Fprintf (staticcheck)
- Add ReadHeaderTimeout to http.Server (gosec)
- Remove unused types and functions (unused)
- Add nolint comments for intentional patterns (InsecureSkipVerify,
  math/rand for jitter, dialect-only SQL formatting)

internal/tui/tab_nodes.go

@@ -2,8 +2,6 @@ package tui
 
 import (
 	"fmt"
-	"go-upkeep/internal/models"
-	"strings"
 	"time"
 )
 
@@ -71,26 +69,3 @@ func fmtNodeLastSeen(t time.Time) string {
 	}
 	return fmt.Sprintf("%dh ago", int(ago.Hours()))
 }
-
-func fmtProbeRegions(site models.Site, probeResults map[string]probeStatus) string {
-	if len(probeResults) == 0 {
-		return subtleStyle.Render("—")
-	}
-	var parts []string
-	for region, status := range probeResults {
-		short := region
-		if len(short) > 6 {
-			short = short[:6]
-		}
-		if status.isUp {
-			parts = append(parts, specialStyle.Render(short+":UP"))
-		} else {
-			parts = append(parts, dangerStyle.Render(short+":DN"))
-		}
-	}
-	return strings.Join(parts, " ")
-}
-
-type probeStatus struct {
-	isUp bool
-}

internal/tui/tab_sites.go

@@ -301,10 +301,10 @@ func fmtStatus(status string, paused bool, inMaint bool) string {
 	if inMaint {
 		return maintStyle.Render("MAINT")
 	}
-	switch {
-	case status == "DOWN" || status == "SSL EXP":
+	switch status {
+	case "DOWN", "SSL EXP":
 		return dangerStyle.Render(status)
-	case status == "PENDING":
+	case "PENDING":
 		return subtleStyle.Render(status)
 	default:
 		return specialStyle.Render(status)
@@ -721,7 +721,7 @@ func (m Model) viewDetailPanel() string {
 	b.WriteString(breadcrumb + "\n\n")
 
 	row := func(label, value string) {
-		b.WriteString(fmt.Sprintf("  %-16s %s\n", subtleStyle.Render(label), value))
+		fmt.Fprintf(&b, "  %-16s %s\n", subtleStyle.Render(label), value)
 	}
 
 	row("Status", fmtStatus(site.Status, site.Paused, m.isMonitorInMaintenance(site.ID)))
@@ -780,7 +780,7 @@ func (m Model) viewDetailPanel() string {
 			}
 			latency := time.Duration(result.LatencyNs).Milliseconds()
 			ago := time.Since(result.CheckedAt).Truncate(time.Second)
-			b.WriteString(fmt.Sprintf("  %-14s %s  %dms  %s ago\n", nodeID, status, latency, ago))
+			fmt.Fprintf(&b, "  %-14s %s  %dms  %s ago\n", nodeID, status, latency, ago)
 		}
 	}
 
@@ -795,9 +795,9 @@ func (m Model) viewDetailPanel() string {
 					up++
 				}
 			}
-			b.WriteString(fmt.Sprintf("\n  %s %d/%d checks up",
+			fmt.Fprintf(&b, "\n  %s %d/%d checks up",
 				subtleStyle.Render("Heartbeats"),
-				up, len(hist.Statuses)))
+				up, len(hist.Statuses))
 		}
 	} else {
 		b.WriteString("  " + latencySparkline(hist.Latencies, sparkWidth))
@@ -814,10 +814,10 @@ func (m Model) viewDetailPanel() string {
 				}
 			}
 			avg := total / time.Duration(len(hist.Latencies))
-			b.WriteString(fmt.Sprintf("\n  %s %dms  %s %dms  %s %dms",
+			fmt.Fprintf(&b, "\n  %s %dms  %s %dms  %s %dms",
 				subtleStyle.Render("Min"), minL.Milliseconds(),
 				subtleStyle.Render("Avg"), avg.Milliseconds(),
-				subtleStyle.Render("Max"), maxL.Milliseconds()))
+				subtleStyle.Render("Max"), maxL.Milliseconds())
 		}
 	}
 

internal/tui/tui.go

@@ -264,20 +264,21 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			if msg.Button == tea.MouseButtonWheelUp || msg.Button == tea.MouseButtonWheelDown {
 				if m.state == stateLogs {
 					if msg.Button == tea.MouseButtonWheelUp {
-						m.logViewport.LineUp(3)
+						m.logViewport.ScrollUp(3)
 					} else {
-						m.logViewport.LineDown(3)
+						m.logViewport.ScrollDown(3)
 					}
 					return m, nil
 				}
 				listLen := len(m.sites)
-				if m.currentTab == 1 {
+				switch m.currentTab {
+				case 1:
 					listLen = len(m.alerts)
-				} else if m.currentTab == 3 {
+				case 3:
 					listLen = len(m.nodes)
-				} else if m.currentTab == 4 {
+				case 4:
 					listLen = len(m.maintenanceWindows)
-				} else if m.currentTab == 5 {
+				case 5:
 					listLen = len(m.users)
 				}
 				if msg.Button == tea.MouseButtonWheelUp {
@@ -364,7 +365,7 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				}
 			case "up", "k":
 				if m.state == stateLogs {
-					m.logViewport.LineUp(1)
+					m.logViewport.ScrollUp(1)
 				} else if m.cursor > 0 {
 					m.cursor--
 					if m.cursor < m.tableOffset {
@@ -373,7 +374,7 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				}
 			case "down", "j":
 				if m.state == stateLogs {
-					m.logViewport.LineDown(1)
+					m.logViewport.ScrollDown(1)
 				} else {
 					max := len(m.sites) - 1
 					if m.currentTab == 1 {
@@ -645,13 +646,14 @@ func (m *Model) refreshData() {
 	m.logViewport.SetContent(strings.Join(m.engine.GetLogs(), "\n"))
 
 	listLen := len(m.sites)
-	if m.currentTab == 1 {
+	switch m.currentTab {
+	case 1:
 		listLen = len(m.alerts)
-	} else if m.currentTab == 3 {
+	case 3:
 		listLen = len(m.nodes)
-	} else if m.currentTab == 4 {
+	case 4:
 		listLen = len(m.maintenanceWindows)
-	} else if m.currentTab == 5 {
+	case 5:
 		listLen = len(m.users)
 	}
 	if listLen > 0 && m.cursor >= listLen {
@@ -709,11 +711,12 @@ func (m Model) View() string {
 	switch m.state {
 	case stateConfirmDelete:
 		kind := "monitor"
-		if m.deleteTab == 1 {
+		switch m.deleteTab {
+		case 1:
 			kind = "alert"
-		} else if m.deleteTab == 4 {
+		case 4:
 			kind = "maintenance window"
-		} else if m.deleteTab == 5 {
+		case 5:
 			kind = "user"
 		}
 		msg := dangerStyle.Render(fmt.Sprintf("Delete %s \"%s\"?", kind, m.deleteName))