feat: add provider_name column to aibridge interceptions (#23960)

## Description

Adds `provider_name` to aibridge interceptions to store the provider
instance name alongside the provider type. This allows distinguishing
between multiple instances of the same provider type (e.g. `copilot` vs
`copilot-business`).

## Changes

* Add `provider_name` column to `aibridge_interceptions` table with
backfill from `provider`.
* Add `provider_name` field to the proto `RecordInterceptionRequest`
message.
* Add `ProviderName` to the `codersdk.AIBridgeInterception` API
response.

_Disclaimer: initially produced by Claude Opus 4.6, modified and
reviewed by @ssncferreira ._

coderd/database/models.go

@@ -4038,6 +4038,8 @@ type AIBridgeInterception struct {
 	ClientSessionID sql.NullString `db:"client_session_id" json:"client_session_id"`
 	// Groups related interceptions into a logical session. Determined by a priority chain: (1) client_session_id — an explicit session identifier supplied by the calling client (e.g. Claude Code); (2) thread_root_id — the root of an agentic thread detected by Bridge through tool-call correlation, used when the client does not supply its own session ID; (3) id — the interception's own ID, used as a last resort so every interception belongs to exactly one session even if it is standalone. This is a generated column stored on disk so it can be indexed and joined without recomputing the COALESCE on every query.
 	SessionID string `db:"session_id" json:"session_id"`
+	// The provider instance name which may differ from provider when multiple instances of the same provider type exist.
+	ProviderName string `db:"provider_name" json:"provider_name"`
 }
 
 // Audit log of model thinking in intercepted requests in AI Bridge