[Frontend][Board] Add width, collapse, and titles-only controls

[Chris0Jeky]

Problem

The v0.2 board slice keeps board context through a side inspector and adds compact density. Width controls, collapsed columns, and titles-only presentation add separate drag/drop, persistence, and accessibility risk.

Scope

• Add bounded column-width preferences.
• Add accessible collapsed columns.
• Add a titles-only density mode after comfortable and compact behavior is proven.
• Preserve ordering, filters, keyboard navigation, realtime refresh, and responsive behavior.

Non-goals

• No column wrapping, arbitrary view engine, backend work-item migration, or removal of the v0.2 inspector fallback.

Acceptance

• Preferences persist through the accepted preference seam with safe defaults.
• Collapse and titles-only modes retain keyboard access, focus return, counts, and drag/drop order.
• Representative desktop and mobile viewports have mounted and browser coverage.
• Realtime updates do not silently reopen or reorder collapsed columns.

Cross-cutting contract

Surface	Requirement
Data/migration	None unless the existing preference record is extended additively
API/security	Existing board/card authorization only
Proposal/audit/MCP	No contract change
Export/import/deletion	Preference behavior documented if persisted server-side
Realtime/tests	Board refresh, keyboard, drag/drop, focus, and viewport proof

Dependencies and release

Depends on #2086 M1. v0.3 M2, Priority III.

[Chris0Jeky]

Residuals from #2097 review, deferred to this v0.3 board-controls lane: preserve a constrained independently scrollable inspector height at desktop widths, and move focus into the dialog when an open desktop inspector crosses into the tablet/mobile modal breakpoint. These were nonblocking for the v0.2 M1 data-loss fix.

[Chris0Jeky]

Additional #2097 P2 residuals routed here: keep the density control inside the mobile viewport, restore focus to the newly selected card after an inspector switch, handle rejected comment loads without an unhandled rejection, and retain the already recorded inspector-height and modal-transition focus work.

[Chris0Jeky]

Deferred inspector navigation edge cases from PR #2100 (non-blocking P2):

• keep the latest navigation attempt when discard confirmation is already open;
• avoid stacking route-discard and card-level confirmation dialogs;
• continue a pending navigation after a successful save or delete.

These do not corrupt saved card state, but they can leave navigation cancelled or expose competing modal focus. Keep them in the v0.3 inspector follow-up with the existing focus and responsive residuals.