fix: [#967] Restore trusted keyword with auto-wrap semantics

[milkyskies]

closes #967

Summary

Reverts the throws keyword flip from #965 while keeping the try removal. npm imports are untrusted by default (auto-wrapped in Result<T, Error>). trusted marks safe imports.

import trusted { useState } from "react"    // direct call
import { fetchUser } from "some-lib"         // auto-wrapped in Result<T, Error>

Test plan

• 1291 cargo tests pass
• Clippy clean
• Example apps pass floe fmt/check/build
• Tree-sitter tests pass (42/42)

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