feat: introduce environment-agnostic PyInstaller infrastructure

[brightyorcerf]

Linked issue

• Closes [Task] Establish Reproducible Windows Packaging Pipeline via PyInstaller #394
• Related refactor(deps): separate runtime and Windows-only build dependencies #133 and ci: implement automated quality gating #376 (Stability track infrastructure)

Existing related work reviewed

• Issues/PRs reviewed: feat(ci): add GitHub Actions pipeline with linting and test scaffolding #120, Add Automated Testing Infrastructure for Cross-Platform Development #231, Fix restored-case data file generation bug and introduce pytest-based backend test suite #110, ci: add pytest suite and GitHub Actions pipeline - automated quality gate in the repo - 34 unit tests #204, refactor(deps): separate runtime and Windows-only build dependencies #133
• Finding: refactor(deps): separate runtime and Windows-only build dependencies #133 (refactor(deps): separate runtime and Windows-only build dependencies): Reviewed. refactor(deps): separate runtime and Windows-only build dependencies #133 successfully restructured the dependency files to allow cross-platform pip install.

Overlap assessment

• Classification: New Infrastructure / Distribution.
• Overlapping items: PR refactor(deps): separate runtime and Windows-only build dependencies #133 (Merged).
• Why this is not duplicate/superseded: refactor(deps): separate runtime and Windows-only build dependencies #133 was explicitly labeled as "PR 1 of 3" and was limited to dependency file restructuring. This PR (feat: introduce environment-agnostic PyInstaller infrastructure #395) serves as the functional follow-up, introducing the .spec manifest and runtime path resolution logic (sys._MEIPASS) necessary to actually produce a working bundle.

Why this PR should proceed

While #133 provided the 'ingredients' (dependencies), this PR provides the 'recipe' (the spec file). Without this infrastructure, the Windows-only build tools added in #133 have no instructions on how to actually assemble the MUIOGO binary, specifically regarding the complex mapping of the WebAPP/ directory and solver binaries.

Summary

• What changed: Added muiogo.spec with defensive pathing logic.
• Why: To enable one-click distribution of MUIOGO for non-technical users.

Validation

• Syntax-validated via Python 3 interpreter.
• Path-resolution logic verified locally via static analysis (checked for "Missing" folder resilience).

Documentation

• Docs updated in this PR (or not applicable)
• 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

Exception rationale

• None

[SeaCelo]

We are not planning for a binary yet. I'll keep this as a draft until we have a plan. Please keep the discussion in the issue