feat(import): add stable per-resource source keys to the importer contract

Re-importing an edited document currently has no way to tell an updated
request from a new one, because every import mints fresh model IDs. Give
each imported resource a key that identifies its source element instead,
so a later import can match against what it already created.

`ImportResponse` gains an optional `sourceKeys` map, keyed by the resource
IDs plugins already emit. A parallel map keeps `ImportResources` and the
partial TS types unchanged.

Bundled importers emit keys where the format carries them: Postman item
IDs, Insomnia `_id`s, OpenAPI `operationId` (falling back to the route),
and Yaak model IDs. curl has no identity of its own, so it emits none.

Planning derives a key for anything left over, hashed from the model type,
folder ancestry, and name or method+URL, prefixed `fb:` so later code can
tell derived keys from importer-provided ones. These break when the source
document renames or moves a resource, which is accepted.

Keys land in `ImportPlan.source_keys`, keyed by minted model ID so the
mapping stays lossless, ready for the commit step to persist. Nothing
consumes them yet.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

plugins/importer-insomnia/src/index.ts

@@ -1,6 +1,6 @@
 import type { Context, PluginDefinition } from "@yaakapp/api";
 import YAML from "yaml";
-import { deleteUndefinedAttrs, isJSObject } from "./common";
+import { deleteUndefinedAttrs, isJSObject, sourceKeysFromResources } from "./common";
 import { convertInsomniaV4 } from "./v4";
 import { convertInsomniaV5 } from "./v5";
 
@@ -32,6 +32,10 @@ export function convertInsomnia(contents: string) {
   if (!isJSObject(parsed)) return null;
 
   const result = convertInsomniaV5(parsed) ?? convertInsomniaV4(parsed);
+  if (result == null) return null;
 
-  return deleteUndefinedAttrs(result);
+  return deleteUndefinedAttrs({
+    ...result,
+    sourceKeys: sourceKeysFromResources(result.resources),
+  });
 }