FLOW-7: Emit event on Supervisor rescheduling failure

[liobrasil]

Closes: #138

Description

Adds an explicit on-chain signal when the Supervisor cannot self-reschedule (e.g. insufficient fee vault balance), preventing silent monitoring stoppage.

• Adds SupervisorRescheduleFailed event.
• Emits failure event for insufficient fees, missing/invalid Supervisor capability, or failure to borrow the fee vault.

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the standards mentioned here.
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
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