fix:#386 replace hardcoded HEROKU URL with configurable API_BASE_URL

[Cypher-CP0]

Linked issue

• Closes [Bug] Hardcoded Deployment URL in Base.Class.js #386
• Related fix: replace hardcoded HEROKU URL with env-configurable API_BASE_URL #387

Existing related work reviewed

• Issues/PRs reviewed: fix: replace hardcoded HEROKU URL with env-configurable API_BASE_URL #387 (opened by issue author, same fix direction)
• If none found: N/A

Overlap assessment

• Classification: Independent parallel fix
• Overlapping items: fix: replace hardcoded HEROKU URL with env-configurable API_BASE_URL #387 addresses the same bug
• Why this is not duplicate/superseded: fix: replace hardcoded HEROKU URL with env-configurable API_BASE_URL #387 was opened by the issue author but appears stalled with no maintainer review. This PR provides a clean, minimal fix from an outside contributor.

Why this PR should proceed

• The hardcoded https://osemosys.herokuapp.com/ URL silently breaks all API calls on any non-Heroku deployment. The fix is a single-file, non-breaking change that unblocks cloud and multi-user deployments with zero impact on local dev workflows.

Summary

• What changed: Removed static HEROKU = 0 flag and the hardcoded https://osemosys.herokuapp.com/ URL from WebAPP/Classes/Base.Class.js. apiUrl() now reads from window.API_BASE_URL if set at deploy time, falling back to window.location.origin for local and standard same-origin deployments.
• Why: HEROKU = 1 hardcoded the API target to a specific Heroku app, causing all API calls to silently fail on any other deployment environment. Replacing it with window.API_BASE_URL makes the URL configurable without touching source code, following 12-factor app principles.

Validation

• Tests added/updated (or not applicable)
• Validation steps documented
• Evidence attached (logs/screenshots/output as relevant)

Documentation

• Docs updated in this PR (or not applicable — README notes local-only scope; server deployment docs deferred to follow-up)
• Any setup/workflow changes reflected in repo docs

Scope check

• No unrelated refactors
• Implemented from a feature branch
• Change is deliverable without upstream OSeMOSYS/MUIO dependency
• Base repo/branch is EAPD-DRB/MUIOGO:main (not upstream)

Exception rationale