Phase 5 slice D1 — Dope sheet multi-select + copy/paste/bulk-move

[fernandotonon]

Overview

First chunk of slice D from #260 — the polish that makes the dope sheet (slice C, #372/#373) actually usable for editing more than one keyframe at a time. Defers per-channel rows (D2) and the curve editor + Bezier handles (D3) to their own follow-up issues so this PR stays reviewable.

The original audit comment for slice D bundled everything together; this issue splits it into three sub-slices:

• D1 (this issue): multi-select, copy/paste, bulk move. Data model unchanged — uses Ogre's existing TransformKeyFrame.
• D2 (follow-up): per-channel rows (T.X / T.Y / R.W / etc.) under each bone.
• D3 (follow-up): curve editor + Bezier handles (requires a tangent side-table since TransformKeyFrame has no handle data).

Scope (this slice)

Selection state

• New selectedKeyframes set on the dope sheet's QML view: { bone, time } pairs.
• Click a diamond → replaces selection with just that one (existing behavior preserved).
• Ctrl+click → toggles a diamond in the selection.
• Shift+click → range-select on the same bone (from last clicked to this one).
• Drag a rectangle on empty timeline area → marquee select all diamonds inside the rect (across rows).
• Esc → clear selection.
• Selected diamonds render with a thicker red outline + larger size.

Bulk move

• Dragging any selected diamond moves the whole selection by the same dt.
• Constraint: clamp the bulk delta so no member of the selection lands < 0 or > animation length, and no member collides with an unselected keyframe at the target time.
• Single MoveKeyframesCommand per release — undo brings the entire selection back as one step.

Copy / paste

• New commands/CopyPasteKeyframesCommand — pure paste side; copy itself is just a clipboard string.
• Copy (Ctrl+C while hovering the dope sheet): serialize selected keyframes (bone + relative time + TRS) to JSON in the system clipboard. The earliest selected time becomes t0 so paste is relative.
• Paste (Ctrl+V): parse JSON; for each entry, create a new keyframe at currentSliderTime + (entryTime - t0). Skip entries whose target time would collide with an existing keyframe (warn via Sentry breadcrumb, don't fail). One PasteKeyframesCommand for the batch — undo removes everything pasted.

Controller (C++) additions

• Q_INVOKABLE bool moveKeyframes(QVariantList selection, double dt) — atomic bulk move, undoable.
• Q_INVOKABLE QString serializeKeyframes(QVariantList selection) — clipboard payload (JSON).
• Q_INVOKABLE int pasteKeyframesAt(QString json, double atTime) — returns count actually pasted (skipping collisions).
• New keyframeSelectionChanged() signal so the dope sheet's selection-overlay redraws.

Tests

Pure-data:

• serializeKeyframes round-trip (parse what we wrote and verify shape).
• pasteKeyframesAt rejects when the target collides with existing keyframes.

Ogre fixture:

• moveKeyframes shifts every member by dt; one command on the undo stack.
• MoveKeyframesCommand undo restores all keyframes; redo re-applies.
• Bulk move that would push one selection member past length is clamped (entire selection moves by the maximum legal dt).
• PasteKeyframesCommand round-trips: paste, undo, paste again — count is consistent.

Out of scope (separate issues)

• Per-channel rows (slice D2)
• Bezier handles + curve editor (slice D3)

Acceptance criteria

• Ctrl+click toggles a diamond in/out of the selection
• Shift+click range-selects within a row
• Drag-rectangle on empty timeline marquee-selects across rows
• Esc clears the selection
• Selected diamonds render distinctly (thicker outline / different color)
• Dragging any selected diamond moves the whole selection by the same dt
• Bulk move clamps at clip boundaries; collisions with unselected keyframes block the move
• Ctrl+C with a selection serializes to clipboard (visible via paste in another text app)
• Ctrl+V at a different scrub time pastes the selection at offset, skipping collisions
• Ctrl+Z undoes a bulk move / paste in one step
• Linux CI: 4+ new tests pass; Sonar quality gate stays green

Plan (#260)

Phase 5 audit comment

Follows: #373 (slice C — dope sheet view).