fix(cli): improve contrast for dim phase rows in acpctl TUI (#1578)

## Summary
- `PhaseColor()` used color `240` (very dark gray) for
idle/completed/cancelled/default phases, making entire table rows nearly
invisible on dark terminal backgrounds
- Bumped to color `245` (~60% gray) which is readable while still
looking subdued compared to active/running phases

## Test plan
- [ ] Run `acpctl` TUI and verify idle/completed agent and session rows
are readable on dark backgrounds
- [ ] Verify active/running rows still stand out visually from idle rows

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Style**
* Updated phase status colors in the terminal interface for improved
visibility. Succeeded, completed, cancelled, idle, and default phase
states now display with brighter coloring, enhancing readability and
making status indicators more visually distinct during terminal
operations.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Ambient Code Bot <bot@ambient-code.local>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people

components/ambient-cli/cmd/acpctl/ambient/tui/views/sessions.go

@@ -14,23 +14,23 @@ import (
 //
 //	pending              -> yellow (33)
 //	running / active     -> orange (214)
-//	succeeded / completed -> dim   (240)
+//	succeeded / completed -> light gray (245)
 //	failed               -> red    (31)
-//	cancelled / idle     -> dim    (240)
+//	cancelled / idle     -> light gray (245)
 func PhaseColor(phase string) lipgloss.Color {
 	switch strings.ToLower(phase) {
 	case "pending":
 		return lipgloss.Color("33") // yellow
 	case "running", "active":
 		return lipgloss.Color("214") // orange
 	case "succeeded", "completed":
-		return lipgloss.Color("240") // dim
+		return lipgloss.Color("245") // light gray — readable on dark backgrounds
 	case "failed":
 		return lipgloss.Color("31") // red
 	case "cancelled", "idle":
-		return lipgloss.Color("240") // dim
+		return lipgloss.Color("245") // light gray — readable on dark backgrounds
 	default:
-		return lipgloss.Color("240") // dim
+		return lipgloss.Color("245") // light gray — readable on dark backgrounds
 	}
 }