[Epic] Gemini CLI Project Framework: Decoupling Intent (Plans) from State (Trackers)

## Overview
This epic covers the transition of Gemini-CLI from a linear, single-session assistant into a deterministic, concurrent project manager. By decoupling **Plans** (intent) from **Trackers** (execution state) and structuring them as a **Directed Acyclic Graph (DAG)**, the CLI will allow for safer, parallel task execution using Git worktrees.

## Core Pillars
1. **Plan/Tracker Decoupling**: Separate what needs to be done (Plan) from its current execution state (Tracker).
2. **Project-Level State**: Maintain tracker state in lockable JSON files () to support concurrent subagents.
3. **Physical Isolation**: Use Git worktrees to allow subagents to work on parallel tasks without filesystem collisions.
4. **DAG Orchestration**: Implement a parent-subagent loop that manages dependencies and 'Radius of Impact' for replanning.

## Reference
- **Design Doc**: [go/gcli-dags](https://docs.google.com/document/d/1QLAJHRr-tvyAtoOm0HYX4EayVUAXuaDljoFKFm47C2U/edit)
- **Template Issue**: #18836

## Milestones
- [ ] Core Plan & Tracker DAG Implementation
- [ ] Project-Level State Management with File Locking
- [ ] Git Worktree Isolation & Lifecycle Management
- [ ] Parent-Subagent Orchestration Loop
- [ ] Interactive Terminal UI for DAG Visualization