chore(android): enable StrictMode penaltyDeath in the demo app

[jkmassel]

Closes #488. Configures StrictMode in the demo app's Application.onCreate() with detectAll() + penaltyDeath() on ThreadPolicy and penaltyLog() on VmPolicy, gated on BuildConfig.DEBUG. Release builds are unaffected.

Diverges from the phased Phase 1 / Phase 2 plan in #488 — the original plan was penaltyLog only, with penaltyDeath deferred to a follow-up after the catalogued violations were addressed. We've collapsed both phases into one PR: the library-side violations are wrapped at the demo call sites (per the issue's "no library permits" rule), so penaltyDeath ships green on day one and any future regression crashes the demo immediately.

Demo-side initialization shape

Because penaltyDeath crashes on any violation, the demo had to be restructured so nothing on the main thread touches disk:

• AccountRepository is initialized lazily on Dispatchers.IO behind a Deferred. Its constructor reads filesDir and triggers com.sun.jna.Native.<clinit>, which runs ~8 disk reads while loading the dispatch library.
• A new GutenbergKitApplication.withAccountRepository { ... } helper awaits the deferred and dispatches the call to Dispatchers.IO. All .all() / .store() / .remove() callsites across MainActivity, AuthenticationManager, EditorActivity, PostsListActivity, and SitePreparationViewModel use it.
• SitePreparationViewModel.createEditorService wraps EditorService.create in withContext(IO). Same for EditorService.purge and EditorService.fetchAssetBundleCount.
• SitePreparationActivity.launchEditor moves EditorDependenciesSerializer.writeToDisk into a coroutine before startActivity.
• EditorActivity.onCreate reads dependencies on IO into Compose state and defers setContent until the read completes.

NetworkAvailabilityProvider stays initialized eagerly on the main thread — its constructor only stores a SAM lambda.

Library-side debt the demo wraps around

docs/code/strictmode.md lists the library-internal disk I/O the demo wraps in withContext(IO) rather than fixing upstream:

• EditorService.create (sync EditorHTTPClient SSL setup + Paths.cacheRoot / storageRoot / defaultTempStorageRoot + EditorURLCache.<init> + EditorAssetsLibrary.<init>).
• EditorService.fetchAssetBundleCount / EditorAssetsLibrary.readAssetBundles.
• EditorDependenciesSerializer.writeToDisk / readFromDisk.

Each is a candidate for a follow-up that moves the I/O off the caller's thread or exposes a suspend API. Library fixes are out of scope here per #488.

Test plan

Verified on a Pixel 9 (Android 16) and an Android 14 emulator. Zero ThreadPolicy violations, no crashes:

• App cold launch — emulator (no saved accounts) and Pixel 9 (saved account, Keystore decrypt path)
• Tap Standalone editor → SitePreparationActivity loads
• Tap Prepare Editor → editor dependencies load
• Tap Start → EditorActivity loads, editor renders
• Type into the editor
• ./gradlew :app:compileDebugKotlin — clean
• The full demo flow listed in Enable strict StrictMode in the Android demo app #488 (connected sites, native inserter sheet, photo permission paths, search, overflow menu, backgrounding) — left for incremental verification as those flows are walked through. Any new flag = wrap at the demo level (docs/code/strictmode.md documents the convention).

Files changed

• android/app/src/main/java/com/example/gutenbergkit/GutenbergKitApplication.kt — StrictMode setup, Deferred<AccountRepository>, withAccountRepository helper.
• android/app/src/main/java/com/example/gutenbergkit/MainActivity.kt — load saved accounts in lifecycleScope, dispatch delete to IO.
• android/app/src/main/java/com/example/gutenbergkit/AuthenticationManager.kt — take GutenbergKitApplication instead of AccountRepository; dispatch store/all paths to IO.
• android/app/src/main/java/com/example/gutenbergkit/SitePreparationViewModel.kt — createEditorService(...) wrapper, IO dispatch on purge / fetchAssetBundleCount / account lookup.
• android/app/src/main/java/com/example/gutenbergkit/SitePreparationActivity.kt — async launchEditor.
• android/app/src/main/java/com/example/gutenbergkit/EditorActivity.kt — async readFromDisk into Compose state; deferred setContent.
• android/app/src/main/java/com/example/gutenbergkit/EditorActivity.kt, PostsListActivity.kt — IO-dispatched account lookups.
• docs/code/strictmode.md (new) — configuration, demo-side init shape, library debt, verification, conventions.
• docs/code/README.md — link to the new doc.