[Bug] Fix field mapping for backend annotations

[shin-gyeongseon]

Title:

Fix missing field mapping for backend podAnnotations in backend-statefulset.yaml

Description:

Issue Summary:
In the langflow-ide chart, the podAnnotations configured under langflow.backend in values.yaml are not correctly mapped to the backend-statefulset.yaml template. Because of an incorrect variable reference, annotations intended for the backend pods (such as Prometheus scraping configurations) are entirely ignored during Helm rendering.

Expected Behavior:
When a user defines backend-specific annotations (e.g., langflow.backend.podAnnotations) in values.yaml, those annotations should be accurately injected into the metadata section of the resulting backend StatefulSet manifest.

Actual Behavior:
The overrides specified under langflow.backend.podAnnotations are silently ignored. The template incorrectly references .Values.langflow.podAnnotations, which does not match the actual structure defined in the values.yaml hierarchy.

Steps to Reproduce:

1. Add or modify annotations under langflow.backend.podAnnotations in values.yaml (e.g., prometheus.io/scrape: "true").
2. Run helm template test-release . inside the langflow-ide chart directory.
3. Inspect the rendered backend StatefulSet. The specified pod annotations will be missing.

Proposed Solution:
Update the metadata annotations section in backend-statefulset.yaml to reference the correct variable path nested under backend.
Change .Values.langflow.podAnnotations to .Values.langflow.backend.podAnnotations.