[Logic] Implement Workspace Persistence

[AlexChesser]

Ticket 1.2: [Logic] Implement Workspace Persistence

Title: Persist Monitor State and Selection across VS Code Sessions

Description:
The ail Monitor currently resets every time VS Code is restarted. We need to use the VS Code Memento API to ensure the user's workspace configuration is remembered.

Tasks:

• Implement ExtensionContext.workspaceState to cache the URI of the last-selected .ail.yaml file.
• Automatically re-load the last active pipeline upon VS Code startup or View expansion.
• (Optional) Persist UI-specific toggles (e.g., which sections were expanded in the Monitor) using the view.description or internal state flags.

Opus Planning Prompt:

"Design a persistence layer for ail using vscode.Memento. Specify which keys should be stored in workspaceState (e.g., lastActivePipelinePath, expandedSections). Plan the 'Rehydration' logic that runs when the WebviewViewProvider is initialized so the user returns to their exact previous state."

[AlexChesser]

✅ Implemented — Workspace persistence complete. Monitor state saved via VS Code Memento API in vscode-ail/src/state.ts using context.workspaceState.get/update().