fix(ios): parse Xcode 27 <tagged-backtrace> in xctrace CPU profile reports

[thymikee]

Purpose

perf cpu profile report fails with Apple xctrace CPU report contained no samples on Xcode 27, even when the trace holds thousands of samples. The Xcode 27 time-profile export wraps each sample's stack in <tagged-backtrace>. The parser only reads <backtrace> (packages/platform-apple/src/core/perf-time-profile.ts:81-88, at fd8277e39), so every row resolves to no stack.

Evidence: Xcode 27.0 beta 6, xctrace 27.0 (27A5252f), iPhone 17 Pro simulator. I ran xctrace record --template 'Time Profiler' --all-processes --time-limit 3s and then exported /trace-toc/run/data/table[@schema="time-profile"]. The export has 38,327 <tagged-backtrace> elements and 0 <backtrace> elements. This predates #2823; main before that PR parses the same export to zero samples.

Required behavior

• The time-profile parser reads the sample stack from <tagged-backtrace> as well as <backtrace>, and resolves ref/id the same way for both.
• Profiles from older Xcode keep parsing unchanged.
• The report output shape does not change.

Completion conditions

• An XML fixture captured from Xcode 27 covers <tagged-backtrace>, and the existing <backtrace> fixture test stays green.
• Live: perf cpu profile start --kind xctrace, then stop, then report on an iOS 27 simulator returns samples. Record the commands in the PR.
• pnpm check:affected --run is green.

[thymikee]

Also confirmed on Xcode 27.1 (27A9269), now the default on the reporting host. A 3 s Time Profiler --all-processes recording on the iPhone 17 Pro simulator, exported through the time-profile schema, has 37,568 <tagged-backtrace> elements and 0 <backtrace> elements. Both Xcode 27.0 and 27.1 need the parser change.

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