Add GET /tests endpoint returning lightweight test summaries (grade,
score, domain, date) with pagination, using database-level JSON
extraction to avoid loading full report blobs. The feature can be
disabled with --disable-test-list flag. Frontend includes a new
/tests/ page with table view and a conditional "History" navbar link.
Fixes: https://github.com/happyDomain/happydeliver/issues/12
Pierre-Olivier Mercier
7422f6ed0a