Fix empty split database metadata reports

[abnegate]

What\n- Treat missing split database metadata collections as empty during Appwrite database-source reports.\n- Add regressions for DocumentsDB reports with no collection metadata table and no indexes metadata table.\n\n## Why\nCloud Backups E2E for DocumentsDB archive reports can request the index resource even when the source collection has no indexes. With DB 6 / split DocumentsDB metadata, counting a missing indexes collection throws Collection not found and leaves the archive pending.\n\n## Validation\n- vendor/bin/phpunit --configuration phpunit.xml tests/Migration/Unit/Sources/AppwriteDatabaseReaderTest.php\n- composer lint\n- composer check\n- docker compose exec tests php vendor/bin/phpunit

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[greptile-apps]

Greptile Summary

Treats a missing split-DB metadata collection as an empty result rather than a fatal error during Appwrite database-source reports, fixing Cloud Backups E2E failures for DocumentsDB archives where the indexes table may not exist.

• Introduces isMissingCollection (using DatabaseNotFoundException subclass check + strcasecmp) and applies it in listTables, listColumns, listIndexes, listRows, and countResources to return []/0 instead of throwing.
• Adds four focused regression tests covering the missing-collection-table and missing-indexes-table report scenarios as well as direct listIndexes/listRows calls.

Confidence Score: 4/5

Safe to merge for the reporting path; the silent-empty behaviour in listColumns and listIndexes during live migration (not just reporting) is the one area worth watching.

The fix is narrowly scoped and correctly typed — it only intercepts DatabaseNotFoundException with an exact case-insensitive message match, so unrelated errors still propagate. The previously raised concern about listRows silently returning [] during live migration applies equally to listColumns (missing attributes = migrated table has no columns) and listIndexes (missing indexes = migrated table has no indexes), both of which also received the silent-empty treatment in this PR. Those paths aren't exercised during reporting, so the archive-pending bug is fixed, but the same masking risk exists on the migration path.

src/Migration/Sources/Appwrite/Reader/Database.php — specifically the listColumns and listIndexes silent-empty paths when called outside the report context.

Important Files Changed

Filename	Overview
src/Migration/Sources/Appwrite/Reader/Database.php	Adds isMissingCollection helper (using DatabaseNotFoundException subclass + strcasecmp) and catches it in five places to return empty results/zero counts when a split-DB metadata collection is absent. The countResources re-throw path preserves pre-existing behavior. The same silent-empty concern previously raised for listRows applies equally to listColumns and listIndexes.
tests/Migration/Unit/Sources/AppwriteDatabaseReaderTest.php	Adds four regression tests covering: missing collection table in report (returns zero counts), missing indexes table in report (returns zero index count), listIndexes returning empty on missing table, and listRows returning empty on missing table. Tests are well-structured and correctly exercise the new guard.

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