feat: add GET /reports endpoint — list previously generated reports w…

[Kaylahray]

feat: add GET /reports endpoint — list previously generated reports with download links

Closes #152

What changed

• generated_reports Postgres table — created on startup via CREATE TABLE IF NOT EXISTS; backfilled from the reports/ directory for any pre-existing files.
• POST /generate-daily-report — now inserts a metadata row (filename, report_date, format, size_bytes, generated_at) into generated_reports after writing each file.
• GET /reports (ADMIN) — returns up to 100 most-recent reports with download_url for each entry.
• GET /reports/download/{filename} (ADMIN) — streams the file as a FileResponse; validates filename against a strict allow-list pattern to prevent path traversal.
• src/types_custom.py — added ReportItem and ReportsListResponse Pydantic models.
• tests/test_reports_list.py — 20+ tests covering empty list, multiple reports, DB error handling, CSV/JSON download, 404, path-traversal rejection, and auth enforcement.

Checklist

• generated_reports table with Postgres-backed metadata
• Startup scan backfills existing files
• GET /reports capped at 100 most recent, ADMIN-gated
• GET /reports/download/{filename} streams file, ADMIN-gated
• Path traversal blocked (400 on invalid filename)
• Tests written for list + download endpoints

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