Add native Android foundation aligned with Wave web design

[LunaStev]

Contributors can now build a native Kotlin/Compose app from android/, with a pinned Gradle toolchain, local API setup instructions, and Android-only CI.

The UI retains the website's original logo, light/dark colors, compact typography, underlined tabs, and grouped document rows. Android adds touch targets and compact/expanded navigation without embedding a WebView.

The runnable slice fetches public XML document catalogs, isolates Wave/Whale paths, merges translations over English, and handles loading, retry, empty results, and stale requests. Article links explicitly open the external browser; full native docs/news readers, accounts, and offline delivery remain separate roadmap work.

Verification

• JDK 17: debug APK, 7 unit tests, lint, and instrumentation APK build.
• English/Korean resource-key parity and staged whitespace checks.
• PR CI: Android build/lint/unit checks, 4 emulator tests including the real launcher, and existing frontend/editor checks.
• Inspect catalog and settings screenshots rendered by the emulator from synthetic fixtures. Screenshots are included in the device report artifact.

Closes #77.
Closes #79.
Closes #80.
Related: #76, #81, #83, #84, #85.