fix(preview): preserve picking and align animated surfaces

[rynfar]

Element picking could stop after an iframe navigated because its one-shot navigation listener was consumed before the main frame changed. Picking now stays armed through subframe navigation and cancels on main-frame navigation, with the listener removed at session cleanup.

Inline preview panels can animate their outer width while the browser slot keeps its own size; the slot now observes the panel too, so its leased surface tracks movement. The sidebar rail uses Pylon's existing shared resize lifecycle, preserving its accepted-width rule and saved width while committing the final pointer position and cleaning up interrupted drags. This selectively adapts upstream 1ab2dfb5, 4cc984fe, and the SidebarRail portion of 46140c96; Pylon already had the shared resize hook.

Verification: 114 focused tests, web and desktop typechecks, scoped lint and formatting. Independent source/test review passed. Live Electron/browser motion was not exercised because this task has no browser/computer-use approval.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	14.0 KiB	13.9 KiB	−38 B (−0.3%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.2 KiB	7.2 KiB	+2 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.8 KiB	6.7 KiB	−40 B (−0.6%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	58.0 KiB	58.0 KiB	−44 B (−0.1%)	66.4 KiB	✅
Codex	Live turn messages	10	9	−1 (−10.0%)	21	✅
Claude	Total thread wire	14.0 KiB	14.0 KiB	−6 B (−0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.2 KiB	7.2 KiB	−5 B (−0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.7 KiB	6.7 KiB	−1 B (−0.0%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.9 KiB	58.9 KiB	−44 B (−0.1%)	66.4 KiB	✅
Claude	Live turn messages	10	9	−1 (−10.0%)	21	✅

Baseline: 7ed3f71 · PR result: 2a88f3b · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 115.6 KiB
• Claude decoded thread snapshot: 116.3 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.