[b-re-w]

Allow theme overrides for overlay geometry, padding, elevation, and scrim effects.

Closes #506

[b-re-w]

macOS Visual Capture Verification (FR-74, #506)

Visual evidence captured off-screen via Skia / Desktop Compose UI test on macOS arm64.

1. Visual Identity Verification (No tokens set)

Comparison between before (develop at 19b63e3f, prior to #511/#512) and after (develop at a2754f1e):

• 512_sheet_default_before.png vs 512_sheet_default_after.png: 0 pixel difference (identical SHA-256 hash).
• 512_dialog_default_before.png vs 512_dialog_default_after.png: 0 pixel difference (identical SHA-256 hash).
• 512_menu_default_before.png vs 512_menu_default_after.png: 0 pixel difference (identical SHA-256 hash).
• Toolkit defaults for corner radius, elevation, padding, and scrim on Sheet, Dialog, and Menu remain identical when no overlay tokens are specified.

Component	File (Before / After)	SHA-256	Byte Diff
Sheet	512_sheet_default_{before,after}.png	50e14bcdd84c1995ae50507c0f0d10a1bfbb5f81c63beeddf4bbe7a7d965144c	0
Dialog	512_dialog_default_{before,after}.png	b2f3f2191cabc0afcacb8a54f38bbf3b3a90e5d012b436a5dddfa1335efc3824	0
Menu	512_menu_default_{before,after}.png	80b5650f3b5eb5e52bdc69f5824e59f4b5ed03569cfac2a923fcc8e364cc8f31	0

2. Overlay Tokens & Scrim in Effect (a2754f1e)

Verification of the new theme tokens and node-level scrim overrides taking effect:

• Sheet: OverlayTokens with sheet_corner_radius(24) (continuous sheet corners), sheet_elevation(16), sheet_padding(24), and node-level .scrim(0x801E3A8A) (dark indigo scrim) taking effect.
• Dialog: OverlayTokens with dialog_corner_radius(24), dialog_elevation(16), dialog_padding(24), and node-level .scrim(0x800F172A) (dark slate scrim) taking effect.
• Menu: OverlayTokens with popup_corner_radius(16), popup_elevation(12), popup_padding(12), and node-level .scrim(0x40000000) taking effect.

Component	Comparison (Default vs Custom FR-74)
Sheet
Dialog
Menu

Artefact Hashes

• 512_sheet_comparison_side_by_side.png (SHA-256: 45931cdfb80a3a4d3fbb8723e323846030aa87477664bfd9c31fadfc4ab5a915)
• 512_sheet_default_before_vs_after.png (SHA-256: 84658e45ca8d2587c7881b8b7201a9652520d53518cc3d1639cbf04f53aca5ba)
• 512_dialog_comparison_side_by_side.png (SHA-256: c93d43b5acf62a84063e39958e95b98f2303a357df2763757f7c11bd29d78aa8)
• 512_menu_comparison_side_by_side.png (SHA-256: 6786792c534e600959eba9c45439ddff2eca5884b7389cc82d08766d9cf14977)
• 512_sheet_custom_after.png (SHA-256: 2b06b759813f94db639e8124fb89baacddcc9c687202628d0db5f98d28599b3f)
• 512_dialog_custom_after.png (SHA-256: ecc2aa915c46e6b8531023bfd64ede4f79845f25ef2c19a89d8fb22b3e18f964)
• 512_menu_custom_after.png (SHA-256: 015716dcfaaea88d236aa2fb4c9485a01f67ac8a3a4c6086504b80733a514d13)