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/collectors/host/disk_test.go

@@ -0,0 +1,80 @@
+package host
+
+import (
+	"syscall"
+	"testing"
+)
+
+func TestParseProcMounts_UnescapesAndParses(t *testing.T) {
+	in := "dev1 / ext4 rw 0 0\n" +
+		"dev2 /path\\040with\\040space xfs rw 0 0\n" +
+		"badline\n"
+
+	ms := parseProcMounts(in)
+	if len(ms) != 2 {
+		t.Fatalf("expected 2 mounts, got %d", len(ms))
+	}
+	if ms[0].MountPoint != "/" || ms[0].FSType != "ext4" {
+		t.Fatalf("unexpected first mount: %+v", ms[0])
+	}
+	if ms[1].MountPoint != "/path with space" {
+		t.Fatalf("expected unescaped mountpoint, got %q", ms[1].MountPoint)
+	}
+}
+
+func TestShouldSkipMount_FiltersPseudo(t *testing.T) {
+	cases := []procMount{
+		{MountPoint: "/proc", FSType: "proc"},
+		{MountPoint: "/sys", FSType: "sysfs"},
+		{MountPoint: "/dev", FSType: "tmpfs"},
+		{MountPoint: "/dev/shm", FSType: "tmpfs"},
+	}
+	for _, c := range cases {
+		if !shouldSkipMount(c) {
+			t.Fatalf("expected skip for %+v", c)
+		}
+	}
+	if shouldSkipMount(procMount{MountPoint: "/home", FSType: "ext4"}) {
+		t.Fatalf("did not expect skip for /home ext4")
+	}
+}
+
+func TestDiskPriority(t *testing.T) {
+	if p, ok := diskPriority(91.9, -1); ok {
+		t.Fatalf("expected no issue, got %v", p)
+	}
+	if p, ok := diskPriority(92.0, -1); !ok || p != "P1" {
+		t.Fatalf("expected P1 at 92%%, got %v ok=%v", p, ok)
+	}
+	if p, ok := diskPriority(97.9, 98.0); !ok || p != "P0" {
+		t.Fatalf("expected P0 if either crosses 98%%, got %v ok=%v", p, ok)
+	}
+}
+
+func TestStatfsCalculations(t *testing.T) {
+	st := syscall.Statfs_t{}
+	st.Bsize = 1
+	st.Blocks = 100
+	st.Bfree = 8
+	st.Bavail = 8
+
+	pct, free := statfsBlockUsedPct(st)
+	if free != 8 {
+		t.Fatalf("expected free=8 bytes, got %d", free)
+	}
+	if pct < 91.9 || pct > 92.1 {
+		t.Fatalf("expected ~92%% used, got %f", pct)
+	}
+
+	st.Files = 100
+	st.Ffree = 2
+	ipct := statfsInodeUsedPct(st)
+	if ipct < 97.9 || ipct > 98.1 {
+		t.Fatalf("expected ~98%% inode used, got %f", ipct)
+	}
+
+	st.Files = 0
+	if statfsInodeUsedPct(st) != -1 {
+		t.Fatalf("expected -1 when inode info unavailable")
+	}
+}