[d-wang-commit]

Description

When tree database root.pg and table database pg coexist, their MTree entries share the internal path root.pg. Merging schemas by that path overwrites the table schema, leaving its maximum RegionGroup counts stale and undercounting databases when calculating other databases' limits.

Key the lookup by TDatabaseSchema.name so both databases participate in adjustment. Explicitly exclude both audit database names during deletion to preserve the existing filtering behavior with the corrected keys.

Tests

• UT: ClusterSchemaManagerTest#testAdjustMaxRegionGroupNumWithMixedModels applies the real adjustment plan and checks both maximum RegionGroup counts for every database as the database count grows from one to three (12 -> 6 -> 4). ConfigManagerDatabaseDeletionTest covers table audit database deletion filtering.
• Validation: Both targeted UTs passed after rebasing onto upstream/master.
• IT: No integration test additions or changes; no IT run for this revision.

Side effects and risks

Correcting the database count may decrease other databases' calculated limits, while preserving already allocated RegionGroups. No serialization or protocol changes.

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This PR has:

• been self-reviewed.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths.

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Key changed/added classes (or packages if there are too many classes) in this PR

• ClusterSchemaInfo: retain both database models in schema lookups.
• ConfigManager: preserve audit database filtering.
• ClusterSchemaManagerTest: verify actual mixed-model limit recalculation and database counting.
• ConfigManagerDatabaseDeletionTest: cover table audit database deletion filtering.

[CRZbulabula]

LGTM!