fix: let exceptions bubble up from getAllManagedIndices() instead of silently returning empty

[Copilot]

getAllManagedIndices() was swallowing all exceptions from getStats() and returning [], causing the cleanup command to silently report "No unused indices found" on connection/auth failures — masking real operational problems.

Changes

• UnusedIndexCleanupService::getAllManagedIndices() — removed the catch (Exception) block; exceptions from SearchIndexServiceInterface::getStats() now propagate up to CleanupUnusedIndicesCommand::execute(), which already handles them by writing the error message to output
• doc/02_Configuration/03_Index_Management.md — resolved merge conflict, keeping improved wording from base branch while retaining the Cleanup Unused Indices section introduced by the PR

// Before: silently hides failures
try {
    $stats = $this->searchIndexService->getStats($indexPrefix . '*');
} catch (Exception) {
    return [];  // ← masks connection errors, auth failures, etc.
}

// After: exception propagates to command for proper error reporting
$stats = $this->searchIndexService->getStats($indexPrefix . '*');

[sonarqubecloud]

Quality Gate failed

Failed conditions
2 New Major Issues (required ≤ 0)

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