Extends resolve_report_period with "year" (year-to-date) and "custom"
(ISO date_from/date_to) keys. Invalid custom bounds fall back to month.
Filter templates now render a GET form around the date inputs so users
can submit an arbitrary range via the calendar-range button; period
pills still drive named periods.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>