refactor(storybook): consolidate dropdown stories into composed controls

docs/sw/storybook-dropdown-consolidation-qa/browser-smoke-release-followup.txt

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+PASS 28 -> 24 SW Stories, exactly four approved Dropdown retirements
+PASS Dropdown group has only Composed Controls with original ID
+PASS all non-SW index entries identical
+PASS all retained declarations identical outside imports, meta and ComposedDemo
+PASS runtime, API, AI template, Overview, existing CSS/assets and Storybook configuration untouched
+PASS User line weight still updates displayed numeric value
+PASS weight mode label preserves the shared numeric value
+PASS details opens existing 28px property Bar
+PASS details opens existing 314px property panel with focus
+PASS property Bar and panel share edited state
+PASS property panel weight edit appears in composed line field
+PASS property panel close returns focus
+PASS property panel Escape returns focus
+PASS narrow details panel keeps natural width and fits viewport
+PASS all seven actionable controls Disabled
+PASS Disabled controls block callbacks and overlays
+PASS callback-free layer icons become readonly status images
+PASS missing detail callback keeps safe no-op and menu open
+PASS retained long layer scenario
+PASS long layer name preserved with full title
+PASS retained many layer scenario
+PASS long layer list scrolls internally
+PASS all 40 user colors accessible with palette scroll
+PASS retained empty layer scenario
+PASS Overview keeps one Header at 49px and 16:9 Stage
+PASS Window Move Motion retains only nine 3x steps
+PASS manager shows Dropdown group with the single Composed Controls page
+PASS retired Dropdown links absent in manager
+PASS no browser console or page errors
+{"status":"PASS","checks":29,"errors":[]}