Sequential approval and execution instead of batch approval queue

### Describe the feature or problem you'd like to solve

Batch approval auto-rejects subsequent operations and prevents iterative step-by-step execution.

### Proposed solution

Change Copilot CLI's execution model to be sequential instead of batch, where each operation is approved/rejected/refined individually before execution, and subsequent operations are planned based on actual results.

**Key improvements:**
- No cascade rejection - each operation is evaluated independently
- User can approve, reject, or refine individual steps before proceeding
- Next steps are planned based on validated results, not assumptions
- Natural iterative workflow that matches how developers think
- Allows course correction between operations without restarting the entire process

This could be implemented as:
- The new default behavior
- An opt-in flag like `--sequential` or `--interactive`
- A configurable setting in `~/.copilot/config.json`

### Example prompts or workflows

**Example 1: Independent operations (current issue)**

Prompt: "Create three text files: notes.txt, todos.txt, ideas.txt"

Current behavior:
1. Create notes.txt [Approve?] ✅
2. Create todos.txt [Approve?] ❌
3. Create ideas.txt [AUTO-REJECTED] ← User wanted this one!

Desired behavior:
1. Create notes.txt [Approve?] ✅ → Executes
2. Create todos.txt [Approve?] ❌ → Skips
3. Create ideas.txt [Approve?] ✅ → Executes

**Example 2: Iterative refinement**

Prompt: "Install the latest versions of React, TypeScript, and ESLint"

Current behavior:
1. Run: npm install react@latest [Approve?] ❌ (User wants specific version 18.2.0)
2. Run: npm install typescript@latest [AUTO-REJECTED]
3. Run: npm install eslint@latest [AUTO-REJECTED]
→ Must restart entire process

Desired behavior:
1. Run: npm install react@latest [Approve?]
User: "Use react@18.2.0 instead"
Run: npm install react@18.2.0 [Approve?] ✅ → Executes
2. Run: npm install typescript@latest [Approve?] ✅ → Executes
3. Run: npm install eslint@latest [Approve?] ✅ → Executes
→ Iterative refinement without restarting

### Additional context

The batch approval model with cascade rejection makes it difficult to work iteratively with Copilot CLI, especially when tasks involve multiple steps that need refinement.