Add temporary capture overlay workflow

[valetivivek]

Summary

Adds a Shottr-style temporary capture overlay workflow for screenshots, with pinned floating captures and explicit save behavior.

Changes

• Adds Temporary capture mode, Overlay timeout, and Copy to clipboard automatically settings.
• Shows temporary captures in-memory without auto-saving or adding history until Save is clicked.
• Adds a floating pinned capture window with copy, save, close, and opacity controls.
• Adds a Copy button to image preview toasts and wires it into the toast button layout designer.
• Tracks saved temporary captures in history after the explicit save path.
• Ignores local .claude/ and .codex-tmp/ directories.

Verification

• dotnet build src/OddSnap/OddSnap.csproj --no-restore -v:minimal
• Build succeeded with 0 warnings and 0 errors.

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[jasperdevs]

dude this is already a thing lol in toast settings