Study Tools Portable v2026.6.15-r33.0

Round 33.0 strengthens local learning-data export and backup usability.\n\n- Adds the export entry to the Windows portable build.\n- Defines a stable schema with schemaVersion, exportedAt, appVersion, source, warnings, and sections.\n- Removes device identifiers and recursively filters password, token, API-key, session, cookie, and secret fields.\n- Keeps valid sections exportable when damaged local JSON is encountered, with localized warnings.\n- Verified real downloads on Windows, Web, online deployment, and 390/430 px mobile viewports.\n\nSHA256: d538da214cdb883392f5236aa3c9c05b88876b9fde3e07ffb4717293329fbb6c