feat(claude): add cost sub-fields and rate limits

[MO2k4]

Summary

• Add TotalAPIDurationMS, TotalLinesAdded, TotalLinesRemoved fields to ClaudeCost struct
• Add ClaudeRateLimits and ClaudeRateLimitWindow structs with nil-safe FiveHourUsage() and SevenDayUsage() helpers returning Percentage
• Add FormattedDuration() and FormattedAPIDuration() methods for human-readable session/API duration
• Document all new properties in the Claude segment MDX docs

Test plan

• All 7 Claude tests pass (TestClaudeSegment, TestClaudeTokenUsagePercent, TestClaudeFormattedCost, TestClaudeFormattedDuration, TestClaudeFormattedAPIDuration, TestClaudeFormattedTokens, TestClaudeRateLimitUsage)
• Rate limit tests cover nil limits, nil windows, nil percentages, rounding, and capping at 100
• Duration tests cover zero, seconds-only, minutes+seconds, exact minute
• Existing test fixture updated with new fields

[AbdelrahmanHafez]

Can't wait to see this go live, let me know if I can help with anything.

[JanDeDobbeleer]

@all-contributors please add @MO2k4 for code,doc

This is pure magic 🪄! @holopin-bot @MO2k4 wizard

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[allcontributors]

@JanDeDobbeleer

I've put up a pull request to add @MO2k4! 🎉