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/details.go

@@ -0,0 +1,105 @@
+package ui
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+	"time"
+
+	"tower/internal/model"
+)
+
+// getRollupSamples extracts sample IDs from a rollup issue's evidence.
+func getRollupSamples(iss model.Issue) []string {
+	samplesStr := iss.Evidence["samples"]
+	if samplesStr == "" {
+		return nil
+	}
+	parts := strings.Split(samplesStr, " | ")
+	result := make([]string, 0, len(parts))
+	for _, p := range parts {
+		p = strings.TrimSpace(p)
+		if p != "" {
+			result = append(result, p)
+		}
+	}
+	return result
+}
+
+// isRollupIssue checks if an issue is a rollup issue.
+func isRollupIssue(iss model.Issue) bool {
+	if strings.HasPrefix(iss.ID, "k8s:rollup:") {
+		return true
+	}
+	if iss.Category == model.CategoryKubernetes && strings.Contains(strings.ToLower(iss.Title), "rollup") {
+		return true
+	}
+	return false
+}
+
+func renderIssueDetails(now time.Time, mode AgeMode, iss model.Issue) string {
+	var b strings.Builder
+
+	fmt.Fprintf(&b, "Title: %s\n", oneLine(iss.Title))
+	fmt.Fprintf(&b, "Priority: %s   Category: %s   State: %s\n", iss.Priority, iss.Category, iss.State)
+	fmt.Fprintf(&b, "FirstSeen: %s\n", fmtTime(iss.FirstSeen))
+	fmt.Fprintf(&b, "LastSeen:  %s\n", fmtTime(iss.LastSeen))
+	fmt.Fprintf(&b, "Age:       %s\n", formatAgeWithMode(iss.Age(now), mode))
+
+	if strings.TrimSpace(iss.Details) != "" {
+		b.WriteString("\nDetails\n")
+		b.WriteString(indentBlock(strings.TrimSpace(iss.Details), "  "))
+		b.WriteString("\n")
+	}
+
+	// Show affected issues for rollup issues
+	if isRollupIssue(iss) {
+		samples := getRollupSamples(iss)
+		if len(samples) > 0 {
+			b.WriteString("\nAffected Issues\n")
+			// Show up to 10 samples
+			maxSamples := 10
+			if len(samples) > maxSamples {
+				samples = samples[:maxSamples]
+			}
+			for _, sample := range samples {
+				fmt.Fprintf(&b, "  • %s\n", sample)
+			}
+		}
+	}
+
+	if len(iss.Evidence) > 0 {
+		b.WriteString("\nEvidence\n")
+		keys := make([]string, 0, len(iss.Evidence))
+		for k := range iss.Evidence {
+			keys = append(keys, k)
+		}
+		sort.Strings(keys)
+		for _, k := range keys {
+			fmt.Fprintf(&b, "  %s: %s\n", k, iss.Evidence[k])
+		}
+	}
+
+	if strings.TrimSpace(iss.SuggestedFix) != "" {
+		b.WriteString("\nSuggested Fix\n")
+		b.WriteString(indentBlock(strings.TrimSpace(iss.SuggestedFix), "  "))
+		b.WriteString("\n")
+	}
+
+	return strings.TrimRight(b.String(), "\n")
+}
+
+func fmtTime(t time.Time) string {
+	if t.IsZero() {
+		return "-"
+	}
+	return t.Local().Format("2006-01-02 15:04:05")
+}
+
+func indentBlock(s, prefix string) string {
+	lines := strings.Split(s, "\n")
+	for i := range lines {
+		lines[i] = prefix + lines[i]
+	}
+	return strings.Join(lines, "\n")
+}