fix(vapor): infer component multi-root metadata from SFC templates for hydration

[edison1105]

This PR makes Vapor hydration consume SSR fragment starts more precisely by adding explicit structural metadata from the compiler instead of relying on runtime heuristics.

On the compiler side, Vapor SFCs now receive __multiRoot metadata, and createIf codegen now carries blockShape so each branch can describe whether it owns a fragment wrapper. On the runtime side, Vapor hydration uses this metadata to determine whether the current belongs to the current component / v-if branch and can be consumed immediately during creation, which fixes several nested multi-root and interop hydration edge cases.

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commit: 132b8eb

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Size Report

Bundles

File	Size	Gzip	Brotli
compiler-dom.global.prod.js	86.4 kB	30.2 kB	26.6 kB
runtime-dom.global.prod.js	110 kB	41.6 kB	37.3 kB
vue.global.prod.js	169 kB	61.4 kB	54.7 kB

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	50.3 kB	19.7 kB	18 kB
createApp	59.3 kB	23 kB	20.9 kB
createApp + vaporInteropPlugin	83.4 kB (+1 B)	30.9 kB (-5 B)	28 kB (+16 B)
createVaporApp	28.8 kB (+5 B)	11.2 kB (+2 B)	10.2 kB (-1 B)
createSSRApp	63.5 kB	24.7 kB	22.4 kB
createVaporSSRApp	32.3 kB (+87 B)	12.5 kB (+64 B)	11.5 kB (+56 B)
defineCustomElement	65.3 kB	24.8 kB	22.5 kB
defineVaporCustomElement	39.2 kB (+88 B)	14.5 kB (+56 B)	13.3 kB (+56 B)
overall	74.2 kB	28.3 kB	25.7 kB