refactor(ui): split IntensitySlider pieces

Extract the slider track, levels, card, and modal into\nfocused subcomponents with shared styles/constants.\nPreserve the existing IntensitySlider API.

.ralph/runs/run-20260125-204012-65223-iter-3.md

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+# Ralph Run Summary
+
+- Run ID: 20260125-204012-65223
+- Iteration: 3
+- Mode: build
+- Story: US-003: Refactor oversized shared components
+- Started: 2026-01-25 21:07:59
+- Ended: 2026-01-25 21:08:01
+- Duration: 2s
+- Status: error
+- Log: /Users/jjbrunton/Projects/Sauci/.ralph/runs/run-20260125-204012-65223-iter-3.log
+
+## Git
+- Head (before): a01079a7c3c6c727a55cd46a72543e86f2378932
+- Head (after): a01079a7c3c6c727a55cd46a72543e86f2378932
+
+### Commits
+- (none)
+
+### Changed Files (commits)
+- (none)
+
+### Uncommitted Changes
+- .agents/tasks/prd-mobile-refactor.json
+- .ralph/activity.log
+- .ralph/runs/run-20260125-204012-65223-iter-2.md
+