chore: remove obsolete files and unused components

[marevol]

Summary

Cleans up obsolete, empty, and auto-generated files that are no longer needed in the project.

Changes Made

• backend/Dockerfile — Remove the testing Docker stage (dataset pre-download step); tests now handle this separately
• backend/recotem/recotem/api/exception_handler.py — Delete empty stub module left from envelope removal refactor
• backend/recotem/recotem/api/forms.py — Delete empty, unused forms module
• create-axios-schema.sh — Delete legacy script for generating axios/openapi schema; superseded by npm run generate:types
• schema.yml — Delete committed auto-generated OpenAPI schema; should not be tracked in version control
• frontend/src/components/common/AppCard.vue — Delete unused shared component
• frontend/src/components/common/PageHeader.vue — Delete unused shared component
• frontend/src/__tests__/components/AppCard.test.ts — Delete test for removed component
• frontend/src/__tests__/components/PageHeader.test.ts — Delete test for removed component
• recotem-sample-image.png — Delete stale sample image asset
• vetur.config.js — Delete Vetur configuration (outdated Vue tooling config, replaced by Volar)

Testing

No functional changes — all deletions. Existing tests remain unaffected.

Breaking Changes

None. All removed files were either empty stubs, auto-generated artifacts, or components confirmed unused.