Single by default (one <input> + '...' toggle reveals the second).
In single mode the JS mirrors From into the hidden To on every
change, so form submit sends adj_date_from=adj_date_to=X for an
exact-day filter on the backend (contract unchanged).
Four presets: Today (single), This week (Mon-Sun range), This month
(1st to last, range), Clear. Presets auto-switch mode so users see
what was populated.
On page load, range mode is inferred from the URL: if both dates
present AND differ -> range mode; else single mode. That way a
bookmarked range URL still shows both pickers.
No backend changes, no new tests — the 8 existing adjustments tests
already cover the from/to contract shape.
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