sdk: return on every path and enforce noImplicitReturns

Apps that set noImplicitReturns fail to typecheck once they import electrobun/main or electrobun/view. The devkit ships .ts source, so tsc checks it with the app's flags, and skipLibCheck doesn't cover .ts. Refs #516.

send() in createTransport returns from try but not from catch. webviewEventHandler returns { success: false } on one path only, and all callers ignore the result. This makes both explicit, with no runtime change, and turns on noImplicitReturns in package/tsconfig.json so the typecheck gate catches new cases.

hutch typecheck in package/: with the flag added, main fails with the 2 TS7030 errors; this branch passes. Unit tests (src/shared src/sdks/main src/config src/preload): 599 pass, 0 fail.