feat: post-outline Approve/Deny buttons for Pause & Outline Plan

[nathanschram]

After user clicks 'Pause & Outline Plan' and Claude writes the outline, Approve/Deny buttons now appear automatically in Telegram. Previously, the user had to type 'approved' in chat, triggering another ExitPlanMode round-trip before buttons appeared.

• Synthetic ActionEvent with Approve/Deny buttons yielded during cooldown auto-deny
• _DISCUSS_APPROVED set tracks sessions where user approved via post-outline buttons
• Next ExitPlanMode call auto-approves when session is in _DISCUSS_APPROVED
• da: callback_data prefix fits 64-byte Telegram limit