fix(claude): keep tool_result blocks first when injecting currentDate

injectClaudeCodeCurrentDate inserted the reminder at index 0 of the first user message. Anthropic requires the message after an assistant tool_use turn to lead with its tool_result blocks, so the request was rejected with 400. Advance the insert index past leading tool_result blocks, matching the existing guard in prependClaudeSystemRemindersToFirstUserMessage. Every other content shape keeps the current index-0 placement.