feat: add CPU limiting and Ralph Loop wizard plan generation

CPU Limiting:
- Add CpuLimitConfig type and settings in App Settings
- Use nice command for process priority (-20 to 19)
- Optional cpulimit integration for hard CPU limits (if installed)
- Applied to new sessions via screen-manager and session modules

Ralph Loop Wizard:
- 3-step wizard: Describe → Plan → Launch
- New /api/generate-plan endpoint generates implementation steps via Claude
- Plan editor with checkboxes, priorities (P0/P1/P2), reordering
- Skip plan option for manual workflows
- Compact wizard modal layout

UI Updates:
- Form section headers for grouped settings
- CPU limit status indicator (cpulimit availability)
- Wizard modal wider layout and inline fields

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/types.ts

@@ -86,6 +86,12 @@ export interface SessionState {
   parentAgentId?: string;
   /** Child agent IDs spawned by this session */
   childAgentIds?: string[];
+  /** CPU limiting enabled */
+  cpuLimitEnabled?: boolean;
+  /** Nice value for CPU priority (-20 to 19) */
+  cpuLimitNiceValue?: number;
+  /** CPU limit percentage (1-100) */
+  cpuLimitPercent?: number;
 }
 
 // ========== Global Stats Types ==========
@@ -233,6 +239,35 @@ export interface AppState {
   tokenStats?: TokenStats;
 }
 
+// ========== CPU Limiting Types ==========
+
+/**
+ * Configuration for CPU limiting of Claude sessions.
+ *
+ * Uses `nice` (always available) to lower process priority and
+ * optionally `cpulimit` (if installed) for hard CPU usage limits.
+ */
+export interface CpuLimitConfig {
+  /** Whether CPU limiting is enabled */
+  enabled: boolean;
+  /** Nice value (-20 to 19, default: 10 = lower priority) */
+  niceValue: number;
+  /** CPU limit percentage (1-100, default: 80) */
+  cpuLimitPercent: number;
+  /** Whether to use cpulimit if available (default: true) */
+  useCpulimitIfAvailable: boolean;
+}
+
+/**
+ * Default CPU limit configuration
+ */
+export const DEFAULT_CPU_LIMIT_CONFIG: CpuLimitConfig = {
+  enabled: false,
+  niceValue: 10,
+  cpuLimitPercent: 80,
+  useCpulimitIfAvailable: true,
+};
+
 // ========== Respawn Controller Types ==========
 
 /**