fix: pass custom instructions to agent when rejecting tool permissions

[CaioDGallo]

Problem

• When rejecting tool permission with custom instructions, the agent was not receiving the custom input. Because of this, it completely ignored any instructions passed and sent them later as a queued message.

Closes #1368

Changes

• Route reject-with-instruction custom input through the permission response instead of sending it as a separate prompt
• Extract and include user feedback in the tool denial message so the agent can act on it

How did you test this?

• Manually