Add filter_url(), a reverse()-style helper that builds a URL to a filtered
list view from a filter object (target inferred from the filter type).
Add OperatorFilter.where(**lookups), a Django-.filter()-style ergonomic
constructor that resolves each field's criterion class from its annotation
(shared with from_json via _criterion_class_for, removing duplication).
Make SessionFilter.timestamp_start/timestamp_end DateCriterion applied via
the __date lookup, so date ranges over the timestamp columns are expressible.
Wire the navbar 'today' / 'last 7 days' totals as links to the matching
filtered session lists, and align the 'last 7 days' total to the same
calendar-day window so the number matches the list it links to.
Stats-table and game-detail links remain a follow-up (see spec).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RF5L4HtbcykTfY9YUYGds3
lukas
