fix(kiro): dedup toolResults + reframe caveman injection

[mydisha]

What

Two fixes for the kiro connector path: dedup tool results before sending to CodeWhisperer/Bedrock, and reframe the caveman style injection so agentic coding tools accept it.

Why

• kiro: CodeWhisperer/Bedrock rejects a userInputMessage whose toolResults list the same toolUseId more than once with TOOL_DUPLICATE (HTTP 400). Duplicates arise from merging consecutive user turns, clients resending tool_result on resume/retry, or the same id appearing as both a RoleTool message and a user-embedded tool_result.
• caveman: the self-identifying sentinel + "caveman mode" framing caused agentic coding tools to treat the guideline as injected content and reject it.

How

• Add dedupKiroUIMToolResults to keep the first occurrence of each toolUseId per userInputMessage; apply to every history user turn and the current message during history construction.
• Remove the sentinel marker and "caveman mode" framing so the guideline reads as part of the operator system prompt; detect idempotency from the directive text via a stable probe substring.
• Regression tests added for the merged-consecutive-turns duplicate case and caveman directive detection.

Checklist

• make test passes
• make vet passes
• npm run lint and npm run typecheck pass (if frontend changed)
• Documentation updated (if applicable)
• Config example updated (if applicable)