ci: bring :app and :e2eTest under the Android Lint gate

[demolaf]

:app and :e2eTest were the two modules #2498 left outside lintAll, since neither declared a lint { } block. Both now join the task, which gates all ten. :e2eTest was already clean; :app reported 30 errors under warningsAsErrors.

• Fixed: SetTextI18n ×4 via a demo_score_row resource, RedundantLabel, UnusedResources ×9 (template colors.xml and two orphaned launcher vectors), ConvertToWebp (firebase_auth to lossless WebP at all five densities, 52KB to 25KB).
• Suppressed in place: AppLinkUrlError ×2, AppLinksAutoVerify, and the facebook_* UnusedResources ×3 — an App Link host and provider strings that per-module lint cannot resolve.
• Disabled for :app, each with its reason in the block: AndroidGradlePluginVersion, LogConditional (same call fix(auth)!: add an Android Lint workflow and gate the Kotlin modules on it #2498 made for :auth), MonochromeLauncherIcon, and KaptUsageInsteadOfKsp — Glide's KSP processor does not generate GlideApp, so that migration means rewriting the storage demo and its README. Following up separately.
• The common disable set and the three strictness flags move to a shared policy in the root build.gradle.kts, beside the existing allprojects checkstyle block — modules keep only their own disables, and strictness is no longer something a module can quietly drop the way :library did. 112 lines out, 56 in.
• lint.yml's google-services.json comment now names :app, which needs that copy for the same reason :proguard-tests does.

Supersedes #2500 (branch renamed).

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Maintainer note: Fixes internal CPRN-433

[gemini-code-assist]

Code Review

This pull request enables Android Lint checks for the :app and :e2eTest modules, integrating them into the root lintAll task and updating the project documentation. It also resolves several lint warnings by extracting hardcoded strings, suppressing specific app link and unused resource warnings, and removing unused assets. The reviewer feedback recommends updating an outdated comment in build.gradle.kts and suggests centralizing the common lint configuration in the root build file to avoid duplication across modules.