fix(ui): stop task cards teleporting when a sidebar toggles

[Limdongcheng]

Summary

Hiding the secondary sidebar teleported every right-anchored task card by the full sidebar width — even a card parked mid-board — and the first stretch of a subsequent drag was silently eaten while the drag origin "caught up" with the card's real position.

Root cause: fit_layout translated a card rigidly with its anchored boundary's displacement, and drag origins were taken from the stored layout rect rather than the rendered one. CardLayout now keeps the user-intended rectangle (preferred) separate from the fitted one: only an edge actually resting on a boundary follows that boundary (the default top-right docking), a parked card keeps its absolute position and is merely clamped inside the new bounds, and a card a sidebar pushed aside returns to its place once the boundary recedes. Drag and resize gestures write both rectangles, so drag origins always match what is on screen.

Validation

• cargo pr-check passes (fmt, source sizes, dependency policy, default-frontends build, clippy -D warnings, reference-backend test suite).
• New full-render regression test drives sidebars, workspace geometry and the Processing card through a hide/drag sequence; fit-level tests pin the parked-stays-put and displaced-returns semantics (task_card_tests.rs).
• Merge with current main is conflict-free (git merge-tree clean).

UI display logic

• New or changed actions go through the command catalog (CommandId + describe) and are searchable in the command palette. (No actions added or changed.)
• Hiding happens only at Ribbon-group level (dataset kind or width budget); transient states disable with a disabled_reason that says how to unblock. (No show/hide logic touched.)
• No layout changes from background events; panels are never auto-closed. (Card geometry now reacts only to explicit sidebar toggles and user drags.)
• New panels or empty regions show an empty state with a next step. (No new panels.)
• Docs updated in docs/ (English and zh-CN) for user-visible behavior. (Bug fix restoring intended drag behavior; no documented behavior changed.)