feat: byok-observability for aibridge (#23808)

## Summary

Adds `credential_kind` and `credential_hint` columns to
`aibridge_interceptions` to record how each LLM request was
authenticated and provide a masked credential identifier for audit
purposes.

This enables admins to distinguish between centralized API keys,
personal API keys, and subscription-based credentials in the
interceptions audit log.

## Changes

- New migration adding `credential_kind`and `credential_hint` to
`aibridge_interceptions`
- Updated `InsertAIBridgeInterception` query and proto definition to
carry the new fields
- Wired proto fields through `translator.go` and `aibridgedserver.go` to
the database

Depends on https://github.com/coder/aibridge/pull/239

coderd/database/modelqueries.go

@@ -869,6 +869,8 @@ func (q *sqlQuerier) ListAuthorizedAIBridgeInterceptions(ctx context.Context, ar
 			&i.AIBridgeInterception.ClientSessionID,
 			&i.AIBridgeInterception.SessionID,
 			&i.AIBridgeInterception.ProviderName,
+			&i.AIBridgeInterception.CredentialKind,
+			&i.AIBridgeInterception.CredentialHint,
 			&i.VisibleUser.ID,
 			&i.VisibleUser.Username,
 			&i.VisibleUser.Name,
@@ -1132,6 +1134,8 @@ func (q *sqlQuerier) ListAuthorizedAIBridgeSessionThreads(ctx context.Context, a
 			&i.AIBridgeInterception.ClientSessionID,
 			&i.AIBridgeInterception.SessionID,
 			&i.AIBridgeInterception.ProviderName,
+			&i.AIBridgeInterception.CredentialKind,
+			&i.AIBridgeInterception.CredentialHint,
 		); err != nil {
 			return nil, err
 		}