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._

coderd/apidoc/docs.go

@@ -163,6 +163,57 @@ const docTemplate = `{
                 ]
             }
         },
+        "/aibridge/sessions": {
+            "get": {
+                "produces": [
+                    "application/json"
+                ],
+                "tags": [
+                    "AI Bridge"
+                ],
+                "summary": "List AI Bridge sessions",
+                "operationId": "list-ai-bridge-sessions",
+                "parameters": [
+                    {
+                        "type": "string",
+                        "description": "Search query in the format ` + "`" + `key:value` + "`" + `. Available keys are: initiator, provider, model, client, session_id, started_after, started_before.",
+                        "name": "q",
+                        "in": "query"
+                    },
+                    {
+                        "type": "integer",
+                        "description": "Page limit",
+                        "name": "limit",
+                        "in": "query"
+                    },
+                    {
+                        "type": "string",
+                        "description": "Cursor pagination after session ID (cannot be used with offset)",
+                        "name": "after_session_id",
+                        "in": "query"
+                    },
+                    {
+                        "type": "integer",
+                        "description": "Offset pagination (cannot be used with after_session_id)",
+                        "name": "offset",
+                        "in": "query"
+                    }
+                ],
+                "responses": {
+                    "200": {
+                        "description": "OK",
+                        "schema": {
+                            "$ref": "#/definitions/codersdk.AIBridgeListSessionsResponse"
+                        }
+                    }
+                },
+                "security": [
+                    {
+                        "CoderSessionToken": []
+                    }
+                ]
+            }
+        },
         "/appearance": {
             "get": {
                 "produces": [
@@ -12778,6 +12829,20 @@ const docTemplate = `{
                 }
             }
         },
+        "codersdk.AIBridgeListSessionsResponse": {
+            "type": "object",
+            "properties": {
+                "count": {
+                    "type": "integer"
+                },
+                "sessions": {
+                    "type": "array",
+                    "items": {
+                        "$ref": "#/definitions/codersdk.AIBridgeSession"
+                    }
+                }
+            }
+        },
         "codersdk.AIBridgeOpenAIConfig": {
             "type": "object",
             "properties": {
@@ -12830,6 +12895,64 @@ const docTemplate = `{
                 }
             }
         },
+        "codersdk.AIBridgeSession": {
+            "type": "object",
+            "properties": {
+                "client": {
+                    "type": "string"
+                },
+                "ended_at": {
+                    "type": "string",
+                    "format": "date-time"
+                },
+                "id": {
+                    "type": "string"
+                },
+                "initiator": {
+                    "$ref": "#/definitions/codersdk.MinimalUser"
+                },
+                "last_prompt": {
+                    "type": "string"
+                },
+                "metadata": {
+                    "type": "object",
+                    "additionalProperties": {}
+                },
+                "models": {
+                    "type": "array",
+                    "items": {
+                        "type": "string"
+                    }
+                },
+                "providers": {
+                    "type": "array",
+                    "items": {
+                        "type": "string"
+                    }
+                },
+                "started_at": {
+                    "type": "string",
+                    "format": "date-time"
+                },
+                "threads": {
+                    "type": "integer"
+                },
+                "token_usage_summary": {
+                    "$ref": "#/definitions/codersdk.AIBridgeSessionTokenUsageSummary"
+                }
+            }
+        },
+        "codersdk.AIBridgeSessionTokenUsageSummary": {
+            "type": "object",
+            "properties": {
+                "input_tokens": {
+                    "type": "integer"
+                },
+                "output_tokens": {
+                    "type": "integer"
+                }
+            }
+        },
         "codersdk.AIBridgeTokenUsage": {
             "type": "object",
             "properties": {