Polish nearby devices and file selection for 0.5.1

[CodePandaaAI]

Why this patch

Version 0.5.0 focused on simplifying discovery behavior. This patch follows through on how that behavior looks and feels.

The Nearby devices section still had pieces that looked separate from each other: its heading, device rows, empty state, and error message. File selection also used large decorative illustrations where clear labels could do the job more directly.

The goal of 0.5.1 is to make these existing interactions feel more consistent without adding another workflow.

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Nearby devices feels like one section

• The heading, device rows, and bottom surface now use coordinated corner shapes and tighter spacing. The rows stay in a single vertical list across screen sizes.
• Discovery errors follow the same visual treatment. Instead of a large error-colored block, the section uses a neutral surface, a small error-colored Wi-Fi badge, centered text, and an outlined Try again button.
• The existing Start/Stop and retry behavior remains in place. These are presentation changes.

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Simpler file selection

• Media and document actions now rely on text and theme colors rather than the camera and document illustrations.
• The media action describes photos and videos, while the document action gives familiar examples. These labels describe the actions; they do not introduce new file-type restrictions.
• Primary and secondary container colors help distinguish the choices. The default shared surface shape also moves to extra-large corners, so the visual adjustment extends to other components that use that default.