azqr copilot — Interactive AI Assistant powered by GitHub Copilot

## Describe the feature
This feature adds a new `azqr copilot` command that starts a conversational AI assistant powered by GitHub Copilot, enabling users to interact with Azure Quick Review using natural language directly from the terminal.

### Features

**Interactive console** — A styled readline-based terminal session with a welcome banner, colored output (blue headers, green prompt, amber tool indicators), and streaming responses as the assistant replies.

**Single-prompt mode** — Run a one-shot query with `--prompt` / `-p` and print the response to stdout, making it scriptable and CI-friendly.

**GitHub Copilot integration** — Connects to GitHub Copilot via the `github/copilot-sdk/go` SDK. Authentication is handled through the GitHub CLI (`gh auth login`).

**Configurable model** — Defaults to `claude-sonnet-4.6`, overridable via `--model`.

**List available models** — `azqr copilot models` lists all models available on the user's Copilot account.

**Full azqr toolset** — The assistant can invoke all azqr tools: `scan`, `scan-carbon-emissions`, `scan-openai-throttling`, `scan-zone-mapping`, `get-recommendations-catalog`, and `get-supported-services`.

**Infinite sessions** — Automatic context compaction (at 80% threshold, hard-stop at 95%) to support long conversations without hitting token limits.

**Microsoft Learn MCP server** — The assistant is connected to the official Microsoft Learn MCP server to fetch up-to-date Azure documentation.

**Graceful shutdown** — Handles `SIGTERM`/`Ctrl+C` cleanly; double `Ctrl+C` within 2 seconds to force-quit.

### Requirements

1. GitHub CLI installed (`https://cli.github.com/`)
2. Authenticated via `gh auth login`
3. Active GitHub Copilot subscription

### Usage

```bash
# Start interactive session
azqr copilot

# Run a single prompt
azqr copilot -p "Scan my Azure subscription for compliance issues"

# Use a specific model
azqr copilot --model claude-sonnet-4.6

# List available models
azqr copilot models
```