perf(desktop-gpui): keep long clip lists responsive

[AksharP5]

Long timelines make the Clips sidebar expensive to redraw because it builds every card, including hundreds outside the viewport. This uses GPUI's existing uniform list to render visible cards and keeps drag targets tied to their timeline indices.

Card rendering stays the same. Scroll limits and the final gap match the existing list. During inline rename, the list keeps all rows mounted so Enter and Escape still work after the input scrolls out of view.

Closes #2704.

Performance

Isolated native GPUI sidebar CPU measurements against current main:

Clips	Before	After
6	0.40 ms	0.39 ms
20	1.24 ms	0.56 ms
100	5.92 ms	0.56 ms
500	39.96 ms	0.56 ms

Median scrolling work at the top of a 390 × 600 viewport. Seven alternating paired runs, 80 scroll events each after warmup, optimized build on an i5-14400F. The probe uses the actual card/list code, bundled assets/fonts, and pinned GPUI with Cap's patches. Starting midway through the list gives the same improvement. This measures component CPU work, excluding media I/O and GPU presentation; it is not a full-app FPS claim.

Validation

• Native app cargo check, formatting and all 24 editor_clips::tests pass.
• Native before/after comparisons match for 96 geometry/scroll snapshots, 88,416 drop-target positions, and Enter/Escape rename actions with the input visible and offscreen. Covers dark/light themes and loaded/placeholder thumbnails.
• Strict Clippy reports the same 27 existing diagnostics on unchanged main and this branch under Rust 1.99, with no new diagnostics.

Checked all 276 open PRs and 211 other open issues, including overlapping file changes and discussions. Found no existing sidebar virtualization work.

Confidence Score: 5/5

The PR appears safe to merge; no actionable issues were found.

Summary

The Clips sidebar now uses uniform_list to build visible cards instead of the entire list.

• The Clips sidebar renders long timelines without building every card.

No actionable issues were found. This review checked source code; it did not run the app or tests.

_{Reviews (1) · Last reviewed commit: "perf(desktop-gpui): keep long clip lists..." · Reviewed by Greptile}

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