Tasks CLI: Add send command #895

Implement coder task send to send new input to a task.

Scope

• Usage: coder task send <task> <--input <text> | stdin> [--wait] [--wait-timeout <dur>]
• Use shared <task> resolver.
• Calls POST /tasks/{id}/send.
• --wait blocks until idle or completed and streams logs while waiting.

Depends on: #891, #902

References: #838