fix(install): remove old DB and gate disk space before download

[kdroidFilter]

Summary

Several Windows users reported the app freezing during the database download. Root cause: the old database (~7.5 GB) + Lucene indexes were not reliably removed before a ~10 GB download + extraction, so the disk filled mid-transfer. On Windows File.delete() returns false silently when a file is locked, the cleanup only scanned the default directory (missing legacy/non-default installs), and the database-update flow had no disk-space gate (unlike onboarding).

The manual workaround was deleting the old DB by hand — this PR automates and guarantees that.

Changes

• DatabaseCleanupUseCase (rewrite): authoritative cleanup targeting the real DB directory (from AppSettings) plus the default one; NIO Files.deleteIfExists so locked files surface a logged exception instead of a silent false; removes seforim.db (+ -wal/-shm), *.lucene, *.lookup.lucene, catalog.pb (previously mis-matched as .proto), lexical.db, release_info.txt, delta-cache, and download leftovers. Returns Success(freedBytes) / Incomplete(undeletable).
• DatabasePreparationUseCase (new): single gate (cleanup + free-space check) that every download/extraction entry point must pass before starting.
• DownloadViewModel: runs the gate before transferring; online + offline screens (onboarding and update) surface a localized "old DB locked" / "insufficient space" message and refuse to start — no more filling the disk.
• PendingDbCleanup (new): records files that couldn't be deleted and retries at the next launch, before the repository opens the DB — automating the manual workaround once the transient (antivirus / Windows Search / leftover handle) lock is gone.
• DatabaseUtils: the database path cache is now resettable, so a reinstall opens the freshly installed DB instead of a stale path.

Notes

• No new nav screen added — the gate is inline via DownloadState.errorKind / prepErrorKind, reusing existing error banners (minimal surface).
• Two new Hebrew strings (db_install_cleanup_failed, db_install_insufficient_space) — wording worth a quick review.

Test plan

• ./gradlew :SeforimApp:compileKotlinJvm (main + test sources)
• ./gradlew :SeforimApp:ktlintCheck :SeforimApp:detekt
• OnboardingFlowIntegrationTest passes
• Manual (Windows): launch with an old/incompatible DB present → update flow removes it and downloads without freezing
• Manual (Windows): simulate a locked old DB → gate shows the "locked" message; restart auto-cleans and the install proceeds
• Manual: low-disk volume → gate shows "insufficient space" instead of starting the download