feat: implement ControlTower TUI for cluster and host monitoring

Add complete TUI application for monitoring Kubernetes clusters and host
systems. Features include:

Core features:
- Collector framework with concurrent scheduling
- Host collectors: disk, memory, load, network
- Kubernetes collectors: pods, nodes, workloads, events with informers
- Issue deduplication, state management, and resolve-after logic
- Bubble Tea TUI with table view, details pane, and filtering
- JSON export functionality

UX improvements:
- Help overlay with keybindings
- Priority/category filters with visual indicators
- Direct priority jump (0/1/2/3)
- Bulk acknowledge (Shift+A)
- Clipboard copy (y)
- Theme toggle (T)
- Age format toggle (d)
- Wide title toggle (t)
- Vi-style navigation (j/k)
- Home/End jump (g/G)
- Rollup drill-down in details

Robustness:
- Grace period for unreachable clusters
- Rollups for high-volume issues
- Flap suppression
- RBAC error handling

Files: All core application code with tests for host collectors,
engine, store, model, and export packages.

internal/ui/table.go

@@ -0,0 +1,131 @@
+package ui
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/charmbracelet/bubbles/table"
+	"tower/internal/model"
+)
+
+// Column keys, used for future sort expansions.
+const (
+	colPri   = "Pri"
+	colCat   = "Cat"
+	colTitle = "Title"
+	colAge   = "Age"
+	colState = "State"
+)
+
+func newIssueTable() table.Model {
+	cols := []table.Column{
+		{Title: colPri, Width: 3},
+		{Title: colCat, Width: 12},
+		{Title: colTitle, Width: 0}, // widened on resize
+		{Title: colAge, Width: 7},
+		{Title: colState, Width: 13},
+	}
+
+	t := table.New(
+		table.WithColumns(cols),
+		table.WithFocused(true),
+		table.WithHeight(10),
+	)
+
+	// Keep built-in styles minimal.
+	s := table.DefaultStyles()
+	s.Header = s.Header.Bold(true)
+	s.Selected = s.Selected.Bold(false)
+	t.SetStyles(s)
+
+	return t
+}
+
+// BuildRows returns table rows and a parallel issue ID slice (row index -> issue ID).
+func buildRows(now time.Time, mode AgeMode, issues []model.Issue) ([]table.Row, []string) {
+	rows := make([]table.Row, 0, len(issues))
+	ids := make([]string, 0, len(issues))
+
+	for _, iss := range issues {
+		age := formatAgeWithMode(iss.Age(now), mode)
+		rows = append(rows, table.Row{
+			iss.Priority.String(),
+			shortCat(iss.Category.String()),
+			oneLine(iss.Title),
+			age,
+			iss.State.String(),
+		})
+		ids = append(ids, iss.ID)
+	}
+	return rows, ids
+}
+
+func shortCat(cat string) string {
+	if cat == "" {
+		return "-"
+	}
+	if len(cat) <= 12 {
+		return cat
+	}
+	// Keep category compact; table has limited width.
+	s := cat
+	if i := strings.IndexByte(cat, ' '); i > 0 {
+		s = cat[:i]
+	}
+	if len(s) > 12 {
+		return s[:12]
+	}
+	return s
+}
+
+func oneLine(s string) string {
+	s = strings.ReplaceAll(s, "\n", " ")
+	s = strings.TrimSpace(s)
+	return s
+}
+
+func formatAge(d time.Duration) string {
+	return formatAgeWithMode(d, AgeCompact)
+}
+
+func formatAgeWithMode(d time.Duration, mode AgeMode) string {
+	if d <= 0 {
+		if mode == AgeRelative {
+			return "0m ago"
+		}
+		return "0s"
+	}
+	if mode == AgeRelative {
+		// Relative format: Xm ago, Xh ago, Xd ago
+		if d < time.Minute {
+			s := int(d / time.Second)
+			return fmt.Sprintf("%ds ago", s)
+		}
+		if d < time.Hour {
+			m := int(d / time.Minute)
+			return fmt.Sprintf("%dm ago", m)
+		}
+		if d < 24*time.Hour {
+			h := int(d / time.Hour)
+			return fmt.Sprintf("%dh ago", h)
+		}
+		days := int(d / (24 * time.Hour))
+		return fmt.Sprintf("%dd ago", days)
+	}
+	// Compact format: 0s, Xds, Xdm, Xdh, Xdd
+	if d < time.Minute {
+		s := int(d / time.Second)
+		return fmt.Sprintf("%ds", s)
+	}
+	if d < time.Hour {
+		m := int(d / time.Minute)
+		return fmt.Sprintf("%dm", m)
+	}
+	if d < 24*time.Hour {
+		h := int(d / time.Hour)
+		return fmt.Sprintf("%dh", h)
+	}
+	days := int(d / (24 * time.Hour))
+	return fmt.Sprintf("%dd", days)
+}