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/querier_test.go

@@ -9085,10 +9085,11 @@ func TestUpdateAIBridgeInterceptionEnded(t *testing.T) {
 
 		for _, uid := range []uuid.UUID{{1}, {2}, {3}} {
 			insertParams := database.InsertAIBridgeInterceptionParams{
-				ID:          uid,
-				InitiatorID: user.ID,
-				Metadata:    json.RawMessage("{}"),
-				Client:      sql.NullString{String: "client", Valid: true},
+				ID:             uid,
+				InitiatorID:    user.ID,
+				Metadata:       json.RawMessage("{}"),
+				Client:         sql.NullString{String: "client", Valid: true},
+				CredentialKind: database.CredentialKindCentralized,
 			}
 
 			intc, err := db.InsertAIBridgeInterception(ctx, insertParams)