feat: implement report caching — skip generation if a report already …

[Kaylahray]

Closes #156

What changed

• src/config.py — added REPORT_CACHE_MINUTES: int = 60 env var with default.
• src/report_service.py — added create_generated_reports_table, insert_report_metadata, and check_report_cache helpers. Updated generate_daily_report_csv signature to accept event_id, force_regenerate, and cache_minutes; returns (path, cache_hit: bool) tuple.
• src/types_custom.py — added event_id and force_regenerate: bool = False to DailyReportRequest; added cache_hit: bool to DailyReportResponse.
• src/main.py — startup now calls create_generated_reports_table; endpoint unpacks the tuple and forwards all new params; response message differs on hit vs miss.
• tests/test_report_caching.py — full test suite: cache hit, cache miss (no engine), stale file fallback, force_regenerate bypasses cache, cache_hit flag in API response, REPORT_CACHE_MINUTES forwarded from settings.
• Updated existing test_daily_report.py and test_standard_modules_unittest.py callers to unpack the new return tuple.

Checklist

• check_report_cache queries generated_reports by {report_date, event_id, format} within REPORT_CACHE_MINUTES
• Cache hit returns existing path with no regeneration
• cache_hit: bool in DailyReportResponse
• force_regenerate: bool skips cache check entirely
• Tests: hit, miss, force regenerate

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