chore: [SDK-4201] migrate from Vite + Bun to Vite+ toolchain

[fadi-george]

Description

1 Line Summary

Migrate the Web SDK build, test, lint, and CI/CD pipeline from Vite + Bun to the Vite+ (vp) unified toolchain.

Details

• Replaces Bun lockfile with pnpm, removes standalone prettier/oxlint configs in favor of vp check
• Consolidates vitest.config.ts into the main vite.config.ts
• Reads sdkVersion directly from package.json instead of relying on npm_package_config_* env vars (which vp run does not set)
• Adds size-limit and vite-plus as direct dev dependencies
• Bundle sizes are ~200 bytes (gzipped) larger due to Rolldown's heavier CJS interop for the jsonp package. Size limits adjusted accordingly.

Note: Linting will fail until a follow-up PR applies formatting fixes (vp check --fix reformats 303 files). This PR intentionally does not include those changes to keep the diff reviewable.

Systems Affected

• WebSDK
• Backend
• Dashboard

Validation

Tests

Info

• All existing tests pass via vp test run --coverage
• Production build output is functionally identical to the previous Vite builds
• CI pipeline updated to use vp commands

Checklist

• All the automated tests pass or I explained why that is not possible
• I have personally tested this on my machine or explained why that is not possible
• I have included test coverage for these changes or explained why they are not needed

Programming Checklist
Interfaces:

• Don't use default export
• New interfaces are in model files

Functions:

• Don't use default export
• All function signatures have return types
• Helpers should not access any data but rather be given the data to operate on.

Typescript:

• No Typescript warnings
• Avoid silencing null/undefined warnings with the exclamation point

Other:

• Iteration: refrain from using elem of array syntax. Prefer forEach or use map
• Avoid using global OneSignal accessor for context if possible. Instead, we can pass it to function/constructor so that we don't call OneSignal.context

Screenshots

Info

N/A — toolchain/build infrastructure change with no UI impact.

Checklist

• I have included screenshots/recordings of the intended results or explained why they are not needed

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Related Tickets

SDK-4201

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