feat: align main exports across node and browser

[SgtPooki]

• add shared FilecoinPinAPI contract and mirror exports in index entries
• consolidate type exports, fix missing dist/index.js
• add isomorphic package import test covering createCarFromPath behavior
• update vitest config to run all tests via multiple projects.
  • individual projects can still be ran via npm run test:unit,
    npm run test:integration, npm run test:browser
  • nodejs tests now run: src/test/unit/**/*.(?iso\.)test.js,
  • new browser tests run: src/test/**/*.(?iso\.)test.js
  • integration tests run: src/test/integration/**/*.test.ts (unchanged)
  • npx vitest run - now runs all three separate projects. Cleaned up npm run test script

Related to #182

[SgtPooki]

self review

[Copilot]

Pull request overview

This PR aligns the main exports between Node.js and browser environments by introducing a shared FilecoinPinAPI contract that both entry points satisfy. The changes consolidate type exports, add an isomorphic package import test, and update the vitest configuration to run tests across multiple projects (unit, integration, and browser).

Key Changes:

• Introduced shared FilecoinPinAPI interface with consistent exports across index.ts and index.browser.ts
• Added multi-project vitest configuration supporting Node.js unit tests, integration tests, and browser tests
• Created isomorphic test pattern (.iso.test.ts) that runs in both Node.js and browser environments

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
vitest.config.ts	Configures three test projects (unit, integration, browser) with appropriate include patterns for each environment
src/test/unit/package-import.iso.test.ts	Adds isomorphic test verifying package imports work correctly in both Node.js and browser environments
src/test/unit/core-data-set.test.ts	Adds biome-ignore comment for vitest mock implementation style
src/index.ts	New Node.js entry point exporting full API including createCarFromPath
src/index.browser.ts	New browser entry point with stub for Node-only createCarFromPath function
src/index-types.ts	Defines shared FilecoinPinAPI interface and re-exports all public types
package.json	Adds browser export conditions, updates test scripts, and adds browser testing dependencies
README.md	Documents the new test:browser npm script

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[SgtPooki]

self review

[rvagg]

I think we should just pick a lane on this and not make it fit everyone's preferences, that's a losing game to play. I'm fine not using default exports, they struggled out of the gate with bad and inconsistent bundler support and I think most people have just got used to not using them. I like explicitness too.