[Task] Absorb selected MUIO v5.6 changes on origin/main

[SeaCelo]

Upstream MUIO has moved past v5.5. Four "MUIO ver 5.6" commits landed in early April, and one more on May 5 reworked the new "indicators" feature. I'm treating that May 5 commit as part of the v5.6 set since it changes the same code.

I checked what it would take to bring this in by simulating the merge from where MUIOGO is today.

This issue is the tracker for that work.

The rule is the same as the v5.5 sync (#388, #393): follow upstream by default, and only deviate where MUIOGO has to keep something working that upstream doesn't care about — portability, security, our setup flow, that kind of thing.

A few things worth knowing up front:

• MUIOGO is still labelled "MUIO 5.5" everywhere; this sync moves us to 5.6
• upstream's current code reads two config files (Indicators.json and Duals.json) that they forgot to commit, so the app crashes on first run if you take it as-is — we'll add small safety checks until upstream ships the missing files
• upstream rewrote the code that finds the GLPK/CBC solver on the user's machine, but their version drops things we'd already fixed in [Bug] Non-Windows solver paths in OsemosysClass are hardcoded dead-end stubs #43, [Bug] Windows .bat installation fails 🦇 #86, fix(windows): improve solver installation flow with CBC fallback (Refs #86) #101, Fix Windows GLPK fallback in setup #262 — we'll keep MUIOGO's version and borrow a few small improvements
• the new "Save" button on the Config page sends extra data that an existing MUIOGO callsite doesn't know to provide; easy to miss, easy to break

The work is split into five sub-issues, sub-PRs target a long-lived feature/v56-ui-sync branch (already pushed), and the final merge from feature/v56-ui-sync to main is the last step (mirrors #422).

Sub-issues:

• [Task] Port HelpersClass.py, Modals.html, and stub Indicators/Duals JSONs for v5.6 #458 [Task] Port HelpersClass.py, Modals.html, and stub Indicators/Duals JSONs (no dependencies — start here)
• [Task] Port indicator frontend for v5.6 #459 [Task] Port indicator frontend (depends on [Task] Port HelpersClass.py, Modals.html, and stub Indicators/Duals JSONs for v5.6 #458)
• [Task] Merge DataFileClass and OsemosysClass for v5.6, keep MUIOGO solver code #460 [Task] Merge DataFileClass and OsemosysClass, keep MUIOGO solver code (depends on [Task] Port HelpersClass.py, Modals.html, and stub Indicators/Duals JSONs for v5.6 #458)
• [Task] Save-path contract for v5.6 (Duals/Indicators data) #461 [Task] Save-path contract — Duals/Indicators data (depends on [Task] Port HelpersClass.py, Modals.html, and stub Indicators/Duals JSONs for v5.6 #458)
• [Task] v5.6 upload/config view, cosmetic changes, and label bump #462 [Task] Upload/Config view, cosmetic changes, and label bump (lands last)

Order: #458 first; #459, #460, #461 can run in parallel after; #462 lands last.

Done when:

• the five sub-issues are closed
• the final PR from feature/v56-ui-sync → main is merged
• ./scripts/setup.sh --check and ./scripts/smoke.sh pass
• demo case solves end-to-end with GLPK and CBC
• a user can add an indicator to a case, save, reload, and still see it
• Versions.html and WebAPP/index.html reflect "MUIO 5.6"

Related:

• [Task] Absorb selected MUIO v5.5 changes on origin/main #388 [Task] Absorb selected MUIO v5.5 changes
• Absorb MUIO v5.5 changes #422 the v5.5 absorb PR
• [Proposal/Architecture] Keep MUIOGO upstream-compatible by default #393 [Proposal/Architecture] Keep MUIOGO upstream-compatible by default
• docs/UPSTREAM_SYNC.md