feat: support config as callback with env context

[2wheeh]

Description

Add callback-style config support.

Changes

1. Pass env from vite.config.ts to resolveVocsConfig()

Before: env was not passed, always defaulted to { command: 'serve', mode: 'development' }

After: Vite's ConfigEnv is forwarded properly (except isSsrBuild - I guess it's not needed for vocs?)

2. Separate defineConfig / resolveConfig

defineConfig: Type helper passthrough:

• Supports env inference for callback usage
• Trade-off: callback overloads take priority, so colorScheme generic only works for object form

resolveConfig: Resolves callback/object and parses config:

• Called by resolveVocsConfig when loading user config
• Referenced Vite's approach: defineConfig, resolveConfig

Since defineConfig is now a passthrough (lazy), parsing happens in resolveVocsConfig via resolveConfig.

Usage

Better support monorepo with tsconfig customConditions resolving exports.source in dev mode:

export default defineConfig(({ mode }) => ({
  vite: {
    resolve: {
      ...(mode === 'development' && {
        conditions: ['source', 'module', 'browser', 'default'],
      }),
    },
  },
}))

(This is actually why I opened this PR)

[vercel]

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[2wheeh]

I will rework based on v2