fix: refresh the Files tab after extracting an archive

[MiMoHo]

Type of change(s)

• Bug fix

What changed and why

When a ZIP is opened from the Files tab, its contents are shown in DecompressActivity, which is launched via an implicit ACTION_VIEW intent (registered for application/zip in the manifest) rather than startActivityForResult. On successful extraction the activity only called toast(R.string.decompression_successful) and finish(), so MainActivity had no way to learn that new content had been written. MainActivity.onResume() never re-reads the current directory and ItemsFragment.onResume() only updates colors/fastscroller/breadcrumb, so the extracted folder only appeared after a manual swipe-to-refresh.

DecompressActivity now records the extracted folder path in a plain-String companion field (extractedFolderPath) on successful extraction. Unlike closed PR #273's companion object var onDecompressFinished: ((String) -> Unit)?, this holds no Activity/lambda reference, so it cannot leak MainActivity. MainActivity.onResume() consumes and clears the field, calling openPath(path, forceRefresh = true) to navigate the Files tab into the freshly extracted folder. Both the write and the read happen on the main thread (runOnUiThread / onResume), so no @Volatile/synchronization is required.

Note: the other decompress entry point (long-press a ZIP -> CAB decompress icon -> ItemsAdapter.decompressSelection) already refreshes via listener?.refreshFragment() and is unaffected by this change.

Tests performed

• detekt, lint, unit tests and the build all pass locally (CI-equivalent).
• Source-verified: after a successful decompression, DecompressActivity records the extracted folder path and MainActivity opens/refreshes that path on return, so the Files tab updates without a manual pull-to-refresh.
• Note: exercised via CI + code review; the extraction UI flow was not scripted end-to-end on the emulator.

Closes the following issue(s)

• Closes Auto-update Files tab content after extracting files from ZIP archive #194

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (verified via CI + source review; see Tests performed).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• I understand every change in this pull request.

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