[WIP] Update dependency tsdown to v0.20.1

[Copilot]

Investigation Summary

The PR fails because tsdown 0.20.1 introduced a regression in how it handles type declaration bundling:

• Identify the failure: check-exports command fails due to unresolved imports in generated .d.mts files
• Root cause: tsdown 0.20.1 now bundles type imports from devDependencies (like Nuxt's #app/defaults) into the generated type definitions
• Found similar issue: rolldown/tsdown#724 - "Version 0.20 throws massive amount of warnings"
• Applied fix: Added external configuration to tsdown.config.ts with patterns to exclude framework-specific imports
• Issue persists: The external config doesn't fully resolve the DTS bundling issue in v0.20.1
• Need alternative solution: Either pin to tsdown 0.18.4 or wait for tsdown fix

Current Status

The external configuration has been added but the build still fails because tsdown 0.20.1's DTS bundler doesn't properly respect the external configuration for certain imports (specifically Nuxt's #app imports that use package.json imports field).

Recommendation

The tsdown dependency update from 0.18.4 to 0.20.1 should be reverted or held until:

1. A new tsdown version fixes this regression, OR
2. A workaround is found to properly exclude devDependency types from DTS bundling

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Project	Deployment	Review	Updated (UTC)
hey-api-docs	Ready	Preview, Comment	Jan 28, 2026 11:20pm

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