Android: reliable private imports and failure recovery

[willlrock]

What changed

• open the Android game library on a normal application launch
• import picker results into persistentDataPath/__Games before parsing
• use read-only streams and typed import failures, with database rollback and staged-file cleanup
• stop treating caught load failures as a reason to call Application.Quit()
• preserve full exceptions in a rotating onlyfun.log
• recover initialization/runtime failures on the Unity thread and return to the library
• make VM stop flags visible across the main and worker threads
• select the exact Honey Cave 2 legacy profile: 101x80, portrait, T310, system 1.30, interpreter, 15 FPS
• discard only the known stale Honey Cave 2 240x320/system 1.50 setting
• add an Editor test assembly covering private import, typed empty-file errors, aliases, and an optional developer-owned external fixture
• add an Android smoke-test checklist

Why

The released Android flow depended on an external intent and a fragile writable content-URI stream. Loader exceptions were discarded and the error dialog's OK action called Application.Quit(), so an ordinary malformed, inaccessible, or unsupported game looked like an application crash. Honey Cave 2 could also inherit the newer 240x320/system 1.50 defaults.

This change keeps external files away from the emulator core, retains actionable diagnostics, and leaves the application usable after failures.

Validation

• git diff master...HEAD --check
• static compile/API audit against Unity 2023.3 APIs
• independent review of stream ownership, error recovery, worker-thread shutdown, and test-assembly references
• inspected both supplied Honey Cave 2 files outside Git: valid VMGP, metadata title HoneyCave2, version 1.0, and no vInit3D import; the files were not committed
• ZIP traversal check before extracting the developer-owned fixtures to a temporary directory

Unity tests and an APK build were not run on this machine. Only Unity Hub is installed; the Editor installation failed for lack of disk space. The project pins Unity 2023.3.0a18, and Android Build Support, SDK/NDK, and OpenJDK are not present.

Known limitations / follow-ups

• ACTION_VIEW, ACTION_SEND, ClipData, and onNewIntent support remain follow-up work
• diagnostics are written to disk, but Copy/Save/Clear diagnostics UI actions are not included yet
• parser hardening and the broader runner state-machine refactor remain separate increments
• the existing CI uses a mismatched Unity version and fork-inaccessible license/keystore secrets; it is not corrected in this PR
• no copyrighted game files are included