Refactor Ralph session tracking with KV-backed session mapping and configurable TTL

[chriswritescode-dev]

Summary

• Replace Ralph sessionId lookups with worktree-keyed KV session mapping
• Add configurable KV TTL with 7-day default
• Improve CLI status with --limit flag and null safety
• Update agent prompts for 7-day TTL

Why

• Eliminate expensive sessionId→worktreeName resolution by storing mapping in KV
• Support configurable TTL for ephemeral state (default 7 days vs 24 hours)
• Prevent KV store bloat by deleting resolved findings instead of updating

What Is Included

• packages/memory/src/services/ralph.ts: registerSession/resolveWorktreeName/unregisterSession
• packages/memory/src/hooks/ralph.ts: Watchdog/stall tracking uses worktreeName keys
• packages/memory/src/index.ts: Plugin integration with new session mapping API
• packages/memory/src/services/kv.ts: Configurable defaultTtlMs parameter
• packages/memory/src/agents/*.ts: Updated prompt text (24h → 7 days)
• packages/memory/src/cli/commands/status.ts: --limit flag, defensive field access
• shared/src/schemas/memory.ts: RalphState fields made required

Type Of Change

• Refactoring
• New feature

Checklist

• Code follows project style
• Types updated
• pnpm lint passes