fix(client): type import.meta.main for run-if-main idioms (#2811)

[viniciusdacal]

Closes #2811.

Summary

Follow-up to #2777. The vtz runtime (via deno_core) already sets import.meta.main on every module — true for the entry module, false for imports — so the standard "run if main" guard works without any polyfill. This PR types it in vertz/client so apps don't need bun-types just to satisfy TypeScript.

// src/api/server.ts
const app = createServer({ /* ... */ });
export default app;

if (import.meta.main) app.listen(env.PORT);  // ✅ typed as boolean

Public API Changes

Addition: ImportMeta.main: boolean declared in packages/ui/client.d.ts. Projects with "types": ["vertz/client"] (or "@vertz/ui/client") get it automatically. Scaffolded apps already have this tsconfig entry.

Declared as mutable (not readonly) on purpose — bun-types declares the same property as main: boolean. Declaration merging requires identical modifiers (TS2687), so matching bun-types avoids a conflict for anyone who keeps both in their tsconfig types.

Breaking / deferred: None.

Changes

• packages/ui/client.d.ts — add main: boolean to ImportMeta.
• packages/ui/src/__tests__/import-meta-hot.test-d.ts, packages/vertz/src/__tests__/import-meta-hot.test-d.ts — flip @ts-expect-error assertions from "not declared" to expectTypeOf<boolean>().
• native/vtz/tests/v8_integration.rs — add test_import_meta_main_true_for_entry_module and test_import_meta_main_false_for_imported_module.
• sites/dev-orchestrator/tsconfig.json + package.json — drop bun-types (only kept for this type; no Bun.* API usage anywhere else). examples/entity-todo keeps bun-types because its test compiler plugin still uses Bun.Transpiler.
• packages/mint-docs/guides/env.mdx, packages/site/pages/guides/env.mdx — document the idiom and tie the type to vertz/client.
• .changeset/import-meta-main-type-2811.md — patch bump for @vertz/ui and vertz.

Acceptance criteria (from #2811)

• Framework stance: Endorse import.meta.main — it's already a runtime guarantee via deno_core; now a typed framework-standard idiom.
• Type augmentation: Added to vertz/client / @vertz/ui/client with JSDoc.
• Migration: Not applicable — call sites continue to use import.meta.main.
• Docs updated: guides/env.mdx (both mint-docs and site) reflect the decision.

Test plan

• cargo test --test v8_integration test_import_meta_main — 2 new Rust integration tests pass (main/side modules).
• vtz test in packages/ui, packages/vertz, packages/create-vertz-app, packages/icons — all green.
• tsc --noEmit in packages/ui, packages/vertz, sites/dev-orchestrator — clean (dev-orchestrator has one pre-existing unrelated error in agent-detail.tsx).
• vtz run format + vtz run lint — clean.
• cargo fmt --all -- --check + cargo clippy --all-targets -- -D warnings — clean.
• Pre-push hooks (build-typecheck, lint, rust-clippy, rust-fmt, rust-test, test, trojan-source) — all green.

Reviews

Adversarial self-review surfaced a latent declaration-merge conflict between readonly main and bun-types' mutable main. Fixed in commit 6117fd9.