fix: recover depth-limited iOS snapshots after AX failures

[thymikee]

Summary

Depth-limited iOS snapshots now recover from XCTest accessibility serialization failures by returning a truncated fallback instead of failing the command outright. AX snapshot errors use the stable IOS_AX_SNAPSHOT_FAILED contract with the existing serialization-tree message prefix, while preserving XCTest details such as kAXErrorIllegalArgument.

The fallback also constrains flat interactive results to the viewport and includes additional visible text/image query types for better sparse discovery when full AX capture is unavailable.

Touched files: 1.

Validation

Verified with pnpm build:xcuitest for both iOS simulator and macOS runner targets. Also ran git diff --check on the touched Swift file. Earlier manual Bluesky probing confirmed depth-limited snapshots return a truncated fallback where full root capture fails.

[github-actions]

Size Report

Metric	Base	Current	Diff
JS raw	1.1 MB	1.1 MB	-3.5 kB
JS gzip	373.2 kB	372.1 kB	-1.1 kB
npm tarball	484.0 kB	483.2 kB	-804 B
npm unpacked	1.6 MB	1.6 MB	-981 B

Startup median (7 runs, lower is better):

Scenario	Base	Current	Diff
CLI --version	23.7 ms	23.7 ms	+0.0 ms
CLI --help	37.5 ms	37.9 ms	+0.4 ms

Top changed chunks:

Chunk	Raw diff	Gzip diff
dist/src/session.js	-1.6 kB	-374 B
dist/src/8699.js	-591 B	-185 B
dist/src/2415.js	-471 B	-108 B
dist/src/1352.js	-316 B	-91 B
dist/src/command-metadata.js	-95 B	-51 B