by-category and daily-spending accept start_date/end_date (range wins
over cycle); Analytics gets a two-month calendar range picker beside
the cycle selector. Fixes a latent float/Decimal TypeError that 500'd
spending_by_category whenever it had data — the category donut had
never rendered. Regression + range tests added.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
