Move __VERSION__ define into root base configs

[Pearce-Ropion]

Summary

• The root package.json and all workspace packages currently share the same version, so the per-package __VERSION__ define was duplicating the root value.
• Moved __VERSION__ into tsdown.base.ts (already there) and added it to vitest.base.ts, then simplified packages/plugin-sdk/{tsdown,vitest}.config.ts to just re-export the base config.

Test plan

• yarn turbo build succeeds and the built bundle still embeds the correct version string at __VERSION__ (verified via packages/plugin-sdk/src/client/initialize.ts).
• yarn turbo test passes — the vitest browser env now picks up __VERSION__ from the root base config.

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Generated by Claude Code

[rilescode]

Would this be an issue if someone manually updates the version in plugin-sdk/package.json without using yarn bump? They could get out of sync

[peternandersson]

I'd rather have this just in the plugin-sdk package since it's the only one that needs the value injected

[Pearce-Ropion]

I'd rather have this just in the plugin-sdk package since it's the only one that needs the value injected

This is prep work for splitting the package into multiple sub-packages. Should each one inject its own version thus requiring duplicated code for each package's tsdown config?

Would this be an issue if someone manually updates the version in plugin-sdk/package.json without using yarn bump? They could get out of sync

This would generally be a problem and that code should not be landed. The whole package should remain in sync.