WT-17116 adds a btree ID uniqueness check that scans local metadata for duplicate IDs among stable constituent files. This ticket extends that check to also verify the shared (disagg) metadata table (file:WiredTigerShared.wt_stable). 

While local metadata should be a superset of shared metadata after the merge, validating shared metadata independently provides an additional safety net - if two table IDs conflict in shared metadata, it indicates corruption that could propagate to any node picking up the checkpoint.

Known blockers to investigate:

• Opening a cursor on the shared metadata checkpoint from within verify causes a checkpoint lock deadlock (WT_WITH_CHECKPOINT_LOCK re-entrancy in
   __wt_session_get_dhandle).
• Directly reading the shared metadata via PALite triggers a page-not-found (SQLITE_NONE) with infinite retry in block_disagg_read.c. Root cause needs
  investigation - may be a PALite-side issue with accessing the shared metadata table during verify.

Reference PoC implementation here.