Replicates zenithprepare.com/PYQ topic-selection UX:
- Subject switcher pills (Maths/Physics/Chemistry) with live selection
counters; only the active subject's chapters are shown.
- Searchable chapter rows with independent subtopic expand arrows
(checking a chapter no longer toggles the tray).
- Complete-syllabus one-click button (selects all 15 units, 75 Qs,
JEE mode).
- Difficulty filter pills (Easy/Medium/Hard, default all) and year
filter pills (2018-2025, default 2020-2025) wired through new
difficulties/years form fields; build_paper filters both, including
the FIFO recycle path. Verified end-to-end: Hard-only paper returns
only Hard questions; Medium+Hard across 2022-2025 leaks zero Easy.
- Settings bar with count pills, JEE-mode toggle and live pool
estimate.
Also fixes: brand header badge, raw-string delimiter clash with SVG
hex fill, Maths subject-key mismatch between pills and DB.
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