feat: persist upstream model capability exclusions

[SakuraPuare]

Summary

• Persist deterministic upstream/model model_not_found exclusions in PostgreSQL.
• Default to permanent exclusions (model_unsupported_ttl=0s), with optional TTL re-probing.
• Apply the same exclusion state to standard and intelligent routing.
• Keep /v1/models positive discovery from clearing negative capability state; hide models only when all discovered group providers are excluded.
• Reuse the existing admin recovery action to delete an exclusion.
• Guard the DDL against replicated schema_migrations rows when schema DDL itself is not replicated.

Validation

• go test ./... passed on the develop host.
• Cherry-picked cleanly from upstream/main at 567cabb.
• Deployed and verified on Home and US MuxAPI clusters.