fix(core): prevent model effect capture in untracked

[andrewiggins]

Summary

• Prevent untracked() from propagating ambient createModel() effect capture into its callback
• Ensure action() callbacks get the same behavior because action() delegates to untracked()
• Add coverage for untracked(), action(), and nested model ownership boundaries

Co-authored by: Pi coding agent & GPT 5.5

[changeset-bot]

🦋 Changeset detected

Latest commit: e823769

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@preact/signals-core	Patch
preact-signals-devtools	Patch

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[github-actions]

Size Change: -7.51 kB (-4.01%)

Total Size: 180 kB

📦 View Changed

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packages/core/dist/signals-core.mjs	1.91 kB	+12 B (+0.63%)
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ℹ️ View Unchanged

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packages/debug/dist/debug.mjs	4.15 kB
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packages/react/dist/signals.mjs	165 B
packages/vite-plugin/dist/vite-plugin.js	8.86 kB
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