feat: session list API (#23202)

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_Disclaimer:_ _initially_ _produced_ _by_ _Claude_ _Opus_ _4\.6,_ _heavily_ _modified_ _and_ _reviewed_ _by_ _me._

Closes https://github.com/coder/internal/issues/1360

Adds a new `/api/v2/aibridge/sessions` API which returns "sessions".

Sessions, as defined in the [RFC](https://www.notion.so/coderhq/AI-Bridge-Sessions-Threads-2ccd579be59280f28021d3baf7472fbe?source=copy_link), are a set of interceptions logically grouped by a session key issued by the client.  
The API design for this endpoint was done in [this doc](https://github.com/coder/internal/issues/1360).

If the client has not provided a session ID, we will revert to the thread root ID, and if that's not present we use the interception's own ID (i.e. a session of a single interception - which is effectively what we show currently in our `/api/v2/aibridge/interceptions` API).

The SQL query looks gnarly but it's relatively simple, and seems to perform well (~200ms) even when I import dogfood's `aibridge_*` tables into my workspace. If we need to improve performance on this later we can investigate materialized views, perhaps, but for now I don't think it's warranted.

---

_The PR looks large but it's got a lot of generated code; the actual changes aren't huge._

docs/reference/api/aibridge.md

@@ -137,3 +137,73 @@ curl -X GET http://coder-server:8080/api/v2/aibridge/models \
 <h3 id="list-ai-bridge-models-responseschema">Response Schema</h3>
 
 To perform this operation, you must be authenticated. [Learn more](authentication.md).
+
+## List AI Bridge sessions
+
+### Code samples
+
+```shell
+# Example request using curl
+curl -X GET http://coder-server:8080/api/v2/aibridge/sessions \
+  -H 'Accept: application/json' \
+  -H 'Coder-Session-Token: API_KEY'
+```
+
+`GET /aibridge/sessions`
+
+### Parameters
+
+| Name               | In    | Type    | Required | Description                                                                                                                                |
+|--------------------|-------|---------|----------|--------------------------------------------------------------------------------------------------------------------------------------------|
+| `q`                | query | string  | false    | Search query in the format `key:value`. Available keys are: initiator, provider, model, client, session_id, started_after, started_before. |
+| `limit`            | query | integer | false    | Page limit                                                                                                                                 |
+| `after_session_id` | query | string  | false    | Cursor pagination after session ID (cannot be used with offset)                                                                            |
+| `offset`           | query | integer | false    | Offset pagination (cannot be used with after_session_id)                                                                                   |
+
+### Example responses
+
+> 200 Response
+
+```json
+{
+  "count": 0,
+  "sessions": [
+    {
+      "client": "string",
+      "ended_at": "2019-08-24T14:15:22Z",
+      "id": "string",
+      "initiator": {
+        "avatar_url": "http://example.com",
+        "id": "497f6eca-6276-4993-bfeb-53cbbbba6f08",
+        "name": "string",
+        "username": "string"
+      },
+      "last_prompt": "string",
+      "metadata": {
+        "property1": null,
+        "property2": null
+      },
+      "models": [
+        "string"
+      ],
+      "providers": [
+        "string"
+      ],
+      "started_at": "2019-08-24T14:15:22Z",
+      "threads": 0,
+      "token_usage_summary": {
+        "input_tokens": 0,
+        "output_tokens": 0
+      }
+    }
+  ]
+}
+```
+
+### Responses
+
+| Status | Meaning                                                 | Description | Schema                                                                                   |
+|--------|---------------------------------------------------------|-------------|------------------------------------------------------------------------------------------|
+| 200    | [OK](https://tools.ietf.org/html/rfc7231#section-6.3.1) | OK          | [codersdk.AIBridgeListSessionsResponse](schemas.md#codersdkaibridgelistsessionsresponse) |
+
+To perform this operation, you must be authenticated. [Learn more](authentication.md).