feat: port DataFile diagnostics UI and ModelFile page from MUIO v5.5

[parthdagia05]

Linked issue

• Closes [Task] Port the DataFile model/log diagnostics from MUIO v5.5 #391
• Related [Task] Absorb selected MUIO v5.5 changes on origin/main #388, [Task] Pull the safe backend/runtime changes from MUIO v5.5 #390

Existing related work reviewed

• Issues/PRs reviewed: [Task] Pull the safe backend/runtime changes from MUIO v5.5 #390 (PR feat: Port safe backend/runtime changes from MUIO v5.5  #397 — backend endpoints), [Task] Absorb selected MUIO v5.5 changes on origin/main #388 (parent tracking issue)
• Upstream MUIO v5.5 source files reviewed via muio-upstream/master

Overlap assessment

• Classification: Sequential dependency — this is the frontend counterpart to [Task] Pull the safe backend/runtime changes from MUIO v5.5 #390 (backend)
• Overlapping items: [Task] Pull the safe backend/runtime changes from MUIO v5.5 #390 added /readModelFile and /readLogFile backend endpoints; this PR adds the frontend that consumes them
• Why this is not duplicate/superseded: [Task] Pull the safe backend/runtime changes from MUIO v5.5 #390 is backend-only. This PR ports the frontend UI that uses those endpoints, plus the standalone ModelFile page and MathJax integration which are entirely new

Why this PR should proceed

• [Task] Port the DataFile model/log diagnostics from MUIO v5.5 #391 is the next sequential child of [Task] Absorb selected MUIO v5.5 changes on origin/main #388 (Absorb MUIO v5.5). The backend prerequisite ([Task] Pull the safe backend/runtime changes from MUIO v5.5 #390) is complete. This delivers the diagnostics UI that upstream v5.5 provides, following upstream by default with no MUIOGO-specific patches needed on the frontend side.

Summary

• What changed:
  • Added readModelFile() and readLogFile() frontend fetch helpers to Osemosys.Class.js
  • Updated DataFile page with LOG FILE button, MODEL FILE button (with modals), and scenario toggle-all control
  • Updated DataFile.Model.js constructor to accept and store modelFile
  • Added Html.renderModelFile() helper
  • Created standalone ModelFile page (Controller/ModelFile.js, Model/ModelFile.Model.js, View/ModelFile.html) that parses GMPL model, converts to LaTeX, and renders equations with MathJax
  • Added MathJax 3 CDN with AMS package to index.html
  • Added /ModelFile route to Routes.Class.js
• Why: Port upstream MUIO v5.5 diagnostics UI into MUIOGO as specified in [Task] Port the DataFile model/log diagnostics from MUIO v5.5 #391 and parent [Task] Absorb selected MUIO v5.5 changes on origin/main #388

Validation

• Tests added/updated (or not applicable) — no existing test suite for frontend; manual validation performed
• Validation steps documented
  • Started app locally with python app.py on Python 3.12
  • Verified /readModelFile endpoint returns 200
  • Verified /readLogFile endpoint returns 404 gracefully (no log file yet — expected)
  • Navigated to #/ModelFile — standalone page renders model equations with MathJax (Objective, Activity, Capacity sections visible with LaTeX formatting)
• Evidence attached — ModelFile page screenshot confirmed during development

Documentation

• Docs updated in this PR (or not applicable) — no doc changes needed; features are self-discoverable UI elements

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

[parthdagia05]

@SeaCelo Could you review this PR.