feat(myopencre): add CSV upload UI and wire to existing import endpoint

[PRAteek-singHWY]

⚠️ This PR depends on:

• feat(myopencre): enable CSV download of all CREs #662 (CSV download of all CREs)

Please review after the above PR is merged.

Summary

Adds the next step of the MyOpenCRE user flow by introducing a frontend UI for CSV upload, allowing users to map their own security standards to OpenCRE without using curl.

This PR wires the existing CSV import backend endpoint to a simple, feature-flagged UI.

⸻

What this PR does

This PR introduces a MyOpenCRE frontend page that allows users to:
• ✅ Download the full CRE catalogue as a CSV
• ✅ Upload a CSV mapping a custom standard (e.g. SOC2) to existing CREs
• ✅ Import mappings via the existing /rest/v1/cre_csv_import endpoint
• ✅ Respect the CRE_ALLOW_IMPORT feature flag:
• Enabled for local execution
• Disabled on hosted OpenCRE (Heroku) to prevent resource abuse

This removes the need to use curl for CSV import/export and makes MyOpenCRE usable by non-technical users.

⸻

Why this is needed

The MyOpenCRE API has been stable for some time, but until now it required manual API usage via curl.

This PR:
• Exposes existing backend functionality through a UI
• Matches the original issue’s acceptance criteria
• Enables the intended user journey for mapping custom standards to CREs

No backend logic is changed — this PR focuses on UI enablement only.

⸻

Scope
• Frontend only
• Uses existing backend endpoints
• No changes to import logic or data model
• No async processing or progress tracking (intentionally out of scope)

⸻

How it was tested
• Ran OpenCRE locally with:
-> export CRE_ALLOW_IMPORT=true
-> make dev-flask

•	Downloaded the CRE catalogue CSV
•	Added a test standard and mapped it to existing CRE IDs
•	Uploaded the CSV via the MyOpenCRE UI
•	Verified successful import response

⸻

Screenshots

⸻

Dependencies

⚠️ This PR depends on:
• #662 – CSV download of all CREs

Please review after the above PR is merged.

⸻

Future work (out of scope for this PR and most probably this issue)

The following are intentionally excluded to keep scope focused and reviewable:
• Async/background CSV import
• Import progress UI
• Improved error UX
• “Dry-run” / validation-only import mode

These are good candidates for follow-up PRs.

[PRAteek-singHWY]

Review focus (apologies for noisy diff)

Apologies for the additional file changes — the actual functionality introduced in this PR is confined to:

• application/frontend/src/pages/MyOpenCRE/MyOpenCRE.tsx
• application/frontend/src/pages/MyOpenCRE/MyOpenCRE.scss
• application/frontend/src/routes.tsx

Other modified files are unrelated to the MyOpenCRE upload flow and were pulled in while rebasing/syncing branches.

Happy to clean these up or move them into a separate PR if that’s preferred.

[PRAteek-singHWY]

This PR is part of the MyOpenCRE frontend flow resolving #584. Full context and next steps are summarized on the issue.