Show file size on each timeline frame

[elkampu]

Goal

Show each captured frame's file size in the Timeline gallery. FrameInfo.SizeBytes already exposes the value, so this should stay in the presentation layer.

Acceptance criteria

• Use the same display contract in both rendering paths: whole KiB below 1 MiB and one decimal MiB at or above 1 MiB. For example, 2,048 bytes displays as 2 KB and 1,572,864 bytes displays as 1.5 MB.
• Server-rendered frame cards and frames added by Load more show the same value.
• Use the existing FrameInfo.SizeBytes field; do not change the frames endpoint shape.
• The layout remains usable at the mobile breakpoint.
• Extend TimelinePageTests to cover the initial server-rendered card and the dynamically constructed Load more card, including a KB and an MB case.

Please comment with your proposed approach before starting. A draft PR is welcome.

[iibaranov-IG]

Proposed approach:

• add one presentation-only size formatter with the requested whole-KB / one-decimal-MB contract
• use it for the initial Razor-rendered frame metadata
• mirror the same threshold and rounding in the existing Load more card builder without changing the frames API
• extend TimelinePageTests with 2,048-byte and 1,572,864-byte files and assert both rendering paths
• keep the size line within the existing responsive metadata block, then run all tests and formatting checks.