docs: correct debug applicationId and google-services.json path

[bmc08gt]

Two build-setup claims in the docs no longer match the build.

Debug applicationId — the docs say debug installs as com.flipcash.app.android.dev. There is no applicationIdSuffix anywhere in the Gradle files; apps/flipcash/app/build.gradle.kts sets applicationId = appNamespace with no per-buildType override, so debug and release share com.flipcash.app.android and installing one replaces the other. Found this the hard way — adb shell monkey -p com.flipcash.app.android.dev returns "No activities found to run".

google-services.json location — the docs point only at apps/flipcash/app/src/. The checked-out copy actually lives at the module root, apps/flipcash/app/, and builds fine from there (processDebugGoogleServices --rerun-tasks passes). CI writes it to src/ (.github/workflows/ci.yml:65) and also passes, so the Google Services plugin accepts either — the docs now say so rather than naming one path.

Same two claims were repeated across CLAUDE.md, docs/architecture/10-build-and-run.md, and docs/architecture/08-cross-cutting-concerns.md.