Add sort controls to Agents / Messages / Locks tree views

[MelbourneDeveloper]

Enhancement

Add user-selectable sort controls to the three TMC tree views. Today every view has a single hard-coded order (and the Agents view has none — tracked as the default-sort bug). Users need to re-sort to find things.

Implement view/title menu commands (view/title contributions in package.json, persisted per-view) that cycle/choose the sort key and direction. Default order in bold.

Agents view — agentsTreeProvider.ts

• Last active (desc) — default (see default-sort bug issue)
• Name (A→Z / Z→A)
• Lock count (desc) — busiest agents first
• Message count (desc)
• Online first (active agents above offline)

Messages view — messagesTreeProvider.ts

Currently hard-coded to createdAt desc with no toggle.

• Time (newest first) — default
• Time (oldest first)
• Unread first
• Sender (fromAgent A→Z)
• Recipient (toAgent A→Z, broadcasts grouped)

Locks / Files view — locksTreeProvider.ts

• Expiry (soonest first) — default
• File path (A→Z)
• Holder (agentName A→Z)
• Active vs. expired grouped

Cross-cutting

• Selected sort persists across refreshes (push events must not reset it) and across reloads (workspaceState/globalState).
• Sort comparators centralized/shared, not duplicated per provider (literals → named constants per repo rules).
• Black-box VS Code extension tests assert ordering for each sort key via vscode.commands.executeCommand.

Spec: see [VSIX-SORT] in docs/spec.md.