feat(perry-ext): #867 — perry/ads MVP (FFI scaffold, structured-failure responses, no SDK linked)

[proggeramlug]

Summary

Mirrors the just-merged #674 @perryts/google-auth cookie-cutter (PR #1028) for the in-app advertising surface. Lands the v1 FFI scaffold for perry/ads so downstream work — real Google Mobile Ads SDK integration, GDPR / ATT consent flow, Info.plist + AndroidManifest auto-injection, the <AdBanner> perry/ui widget glue — can land independently against a stable manifest + codegen surface.

• New crate crates/perry-ext-ads (rlib + staticlib) exposing six FFI entry points:
  • js_ads_interstitial_load(unitId): Promise<string> — JSON {success, error?}
  • js_ads_interstitial_show(): Promise<string> — JSON {shown, dismissed, error?}
  • js_ads_rewarded_load(unitId): Promise<string> — JSON {success, error?}
  • js_ads_rewarded_show(): Promise<string> — JSON {earned, amount?, type?, dismissed, error?}
  • js_ads_banner_create(unitId, sizeKey): number — perry-ffi handle id
  • js_ads_banner_destroy(handle): void
• Wired through every gate: perry-api-manifest NATIVE_MODULES + per-method entries, perry-codegen NATIVE_MODULE_TABLE + runtime_decls (NR_PTR / NR_F64 / NR_VOID), well_known_bindings.toml (perry/ads → libperry_ext_ads.a), and types at types/perry/ads/index.d.ts.
• Every entry point resolves a structured { error: "no-sdk-linked" } placeholder via the standard spawn_blocking + JsPromise::resolve_string pattern bcrypt / argon2 / google-auth use. Platform-specific mod platform { ... } blocks for iOS + macOS, Android, and other-targets carry TODO(Feature request: perry/ads — in-app advertising SDK support #867) markers where the real SDK calls (GADInterstitialAd / GADRewardedAd / GADBannerView on Apple, com.google.android.gms.ads.* on Android) will land.

Scope boundaries (explicitly out of v1)

• No real ad SDK is linked — Apple SwiftPM and Android play-services-ads integration is the larger follow-up tracked under the same issue.
• No <AdBanner> widget in perry/ui — banner handles round-trip through the FFI; widget tree integration is deferred.
• No GDPR / ATT consent flow code.
• No Info.plist / AndroidManifest auto-injection from a [ads] perry.toml block.

Test plan

• cargo build --release -p perry-runtime -p perry-stdlib -p perry -p perry-ext-ads succeeds.
• ./target/release/perry test-files/test_ads_compile_smoke.ts -o /tmp/test_ads_smoke links cleanly and the binary prints all six expected lines:

  interstitial_load: {"success":false,"error":"no-sdk-linked"}
  interstitial_show: {"shown":false,"dismissed":false,"error":"no-sdk-linked"}
  rewarded_load: {"success":false,"error":"no-sdk-linked"}
  rewarded_show: {"earned":false,"dismissed":false,"error":"no-sdk-linked"}
  banner_create: 0
  banner_destroy: ok
  

• CI: lint, cargo-test, parity, compile-smoke, api-docs-drift, security-audit.

Part of #867. Real SDK integration / consent flow / manifest injection follow up on the same issue.