fix: guard the text editor against opening very large files (OOM)

[MiMoHo]

Type of change(s)

• Bug fix

What changed and why

Opening a large text file from the file list crashed the app. ReadTextActivity.checkIntent() reads the entire file into memory before setting it on the EditText. When a file is opened from the File-Manager list, commons openPathIntent adds the REAL_FILE_PATH extra, so the activity builds a file:// Uri and takes the file.readText() branch. That branch only catches Exception, but reading a 100+ MB file throws java.lang.OutOfMemoryError (an Error, not an Exception), so it goes uncaught and the app crashes. (The content:// branch already catches OutOfMemoryError, so the behaviour was inconsistent.) Even if the read succeeded, setText() of such large text on the UI thread would OOM/ANR.

This adds a 1 MB size guard at the start of checkIntent() — the same limit used by Fossify Notes — checked before any read. If the file exceeds the limit, a "File too large, the limit is 1MB" toast is shown and the activity finishes instead of loading the file. The check covers both file:// (via File.length()) and content:// (via getSizeFromContentUri) sources. As requested by @Aga-C on the issue, the message string mirrors Fossify Notes.

Changes:

• ReadTextActivity.kt: add FILE_SIZE_LIMIT = 1000 * 1000 constant and a size check in checkIntent().
• strings.xml: add file_too_large string.
• CHANGELOG.md: note the fix under Unreleased / Fixed and add the [#123] link reference.

No new imports were needed: File is already imported and getSizeFromContentUri, toast and finish are available via the existing org.fossify.commons.extensions.* import.

Tests performed

Built fossDebug, installed on an Android 15 (API 35) emulator.

• Opened a 5 MB text file via the built-in editor (ReadTextActivity): the activity now finishes immediately with a "File too large" toast and no OutOfMemory/crash (logcat clean). Before the fix this OOM-crashed.
• A small text file still opens normally and shows its content in the editor.
• detekt, lint, unit tests and build all pass locally (CI-equivalent).

Closes the following issue(s)

• Closes File Editor: Open .txt crash #123

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator.
• 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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_{Coded with Opus 4.8 ultracode.}