Compact mode: one-line collapsed summaries, density setting, collapsed-by-default for secondary cards #198

Goal

Make a collapsed card still useful, and let the dashboard be dense when the commander wants it.

Scope

• Every card provides a one-line collapsed summary (e.g. Ship: Python MkII - fuel 84% - hold 12/64 t; Missions: 3 active, next expiry 2h), supplied by the card's own view model.
• A density setting (comfortable / compact) affecting padding, font size within the design-system scale, and default widths.
• Sensible defaults: secondary cards start collapsed in new default workspaces; the commander's own choices always win.
• Summaries update live without causing layout jumps (fixed or bounded height; Dashboard cards swap columns on their own (masonry placement follows live card heights) #180).

Acceptance criteria

• Every card has a meaningful, never-empty collapsed summary.
• Switching density does not move cards between columns.
• Contrast and text size stay within the design system.

Part of the epic #194.

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