feat(seer): Send referrer 'api.cli' on autofix API calls (#965)

Add `referrer: "api.cli"` to the POST body for both
`triggerRootCauseAnalysis` and `triggerSolutionPlanning` so the Sentry
backend can attribute autofix runs triggered from the CLI.

### Context

- getsentry/sentry#115497 adds an optional `referrer` field to
`GroupAutofixEndpoint`
- getsentry/sentry#115514 registers the `CLI = "api.cli"` enum value on
`AutofixReferrer`

This PR is the CLI-side counterpart: it sends the `api.cli` referrer
string on every autofix POST so downstream analytics and Seer can
identify CLI-initiated runs.

### Changes

- **`src/lib/api/seer.ts`** — add `referrer: "api.cli"` to the request
body in `triggerRootCauseAnalysis` and `triggerSolutionPlanning`
- **`test/lib/api-client.seer.test.ts`** — update body assertions to
expect the new field

Co-authored-by: Junior <junior[bot]@sentry.io>

Author: sentry-junior[bot]

src/lib/api/seer.ts

@@ -60,6 +60,7 @@ export async function triggerRootCauseAnalysis(
       params: EXPLORER_MODE_PARAMS,
       body: {
         step: "root_cause",
+        referrer: "api.cli",
       },
     }
   );
@@ -125,6 +126,7 @@ export async function triggerSolutionPlanning(
       body: {
         step: "solution",
         run_id: runId,
+        referrer: "api.cli",
       },
     }
   );

test/lib/api-client.seer.test.ts

@@ -71,6 +71,7 @@ describe("triggerRootCauseAnalysis", () => {
 
     expect(capturedBody).toEqual({
       step: "root_cause",
+      referrer: "api.cli",
     });
   });
 
@@ -228,6 +229,7 @@ describe("triggerSolutionPlanning", () => {
     expect(capturedBody).toEqual({
       step: "solution",
       run_id: 12_345,
+      referrer: "api.cli",
     });
   });
 });