upgrade: mutation-observer package upgrade for Solid 2.0

[davedbase]

• Upgrades @solid-primitives/mutation-observer to Solid.js v2.0-beta.10.
• Replaces removed onMount with onSettled so observation begins after the component fully settles (async-aware)
• Switches isServer import to @solidjs/web, removing the manual typeof window check
• Guards start() against missing DOM globals in Node.js environments
• Adds test/server.test.ts to cover SSR safety
• Bumps peer dependencies to solid-js@^2.0.0-beta.10 and `@solidjs/web@^2.0.0-beta.10

[changeset-bot]

🦋 Changeset detected

Latest commit: 975b175

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

This PR includes changesets to release 1 package

Name	Type
@solid-primitives/mutation-observer	Major

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