Reconcile own indices with pre-existing OHDSI-standard indices

[nicoloesch]

• Closes Duplicate indices when a database is already indexed by the official OHDSI CDM DDL script #35

Note before merging

This PR targets the branch staging-overhaul. It depends on ReservedSchema.STAGING / orm_loader.backends.STAGING_SCHEMA, which only exists on staging-overhaul. To restore the history of this branch and exclude the staging changes again, we need to merge it after #29 was merged into main using

git rebase --onto origin/main origin/staging-overhaul index-reconciliation
git push --force-with-lease

Summary

• Adds live, column-set-based reconciliation (_is_plain_index, _find_equivalent_index, _find_shape_conflict in cli_indexes.py) so indexes enable recognizes an index that already exists under a foreign name (e.g. from the official OHDSI CDM DDL script) and never creates a duplicate.
• Adds capture/restore bookkeeping (a dropped_indexes table in a new reserved schema, omop_alchemy_maintenance on PostgreSQL) so indexes disable can safely drop such a foreign-named index for bulk-load speed, and a later indexes enable restores it under its original name. Includes schema-scoping to prevent collisions across two schemas.
• Adds a ReservedSchema StrEnum (_cli_utils.py) centralizing STAGING and MAINTENANCE, guarded via reject_reserved_schema() wired into the omop_command decorator so every maintenance CLI command is protected, not just vocab load-vocab-source.
• Updates cli_schema_reconcile.py so a foreign-named equivalent index reports a single "renamed" issue instead of a misleading "missing" + "unexpected" pair, and doesn't count as drift. This includes the CLUSTER comparison and in the doctor/summary rendering layers.
• Fixes cli_vocab.py's bulk vocabulary loader silently discarding indexes disable's warning results; they now surface on VocabularyLoadReport.index_warnings and render as a dedicated panel.
• Fixes a crash: a second indexes disable run (without an intervening enable) when a different foreign index appears on the same columns now degrades gracefully instead of raising an uncaught IntegrityError.
• Fixes load_vocab_source()'s reserved-schema guard only covering STAGING, not MAINTENANCE, when called directly (bypassing the CLI).
• Extracts a shared _resolve_physical_cluster_name() helper used by both manage_indexes()'s cluster step and the standalone indexes cluster command, fixing a hardcoded unique=False in the latter and removing a duplicated resolution policy that could have drifted out of sync.
• Replaces every ad hoc status: str field across all ten cli_*.py maintenance modules with one shared typed Status StrEnum, each member carrying a Severity (OK/INFO/WARNING/ERROR, itself carrying a render style).
• Relocates FullTextResult/FullTextAction from omop_alchemy/backends/base.py to omop_alchemy/maintenance/cli_fulltext.py.
• Collapses manage_indexes()'s independent Optional outcome locals into a single _IndexOutcome discriminated dataclass, so two of them being set simultaneously by a future edit becomes structurally impossible