fix(mcm): navigator reliability and settings UI fixes

[codepuncher]

Summary

• [MCM-5] Reset g_papyrusEagerScheduled when SKI_ConfigManager is not yet bound, allowing EnsureCachePopulated to retry on the next call rather than wedging permanently
• [MCM-6] Standardize g_modCache write policy in OpenMod to always-overwrite instead of write-once, so a later GFx snapshot supersedes a stale one
• [MCM-7] Fix IsFrameworkInstalled to cache only on a positive result — previously a static const bool evaluated once at startup before the framework was loaded, silently disabling the UI
• [MCM-8] Replace all runtime std::string concatenations for GFx paths with constexpr full-path constants, eliminating per-call heap allocations on navigation and animation-poll paths
• [MCM-9] Snapshot GetCachedModNames once when the mod dropdown opens rather than re-acquiring the mutex on every rendered frame

Part of the June 2026 audit fix series (#51, #52).

Test plan

• Build clean (./scripts/build.sh)
• clang-tidy and clang-format pass (pre-commit hooks)
• In-game: long-press Start/Back → MCM opens and navigates to configured mod
• Settings UI mod dropdown populates and selection persists

[Copilot]

Pull request overview

This PR improves the reliability and performance of MCM navigation and the in-game settings UI by fixing cache invalidation/refresh behaviors and reducing per-frame overhead in GFx path handling and mod-name retrieval.

Changes:

• Fixes SkyUI/framework detection and Papyrus-cache scheduling so MCM caching/navigation can recover from transient initialization states.
• Replaces runtime GFx path string concatenations with constexpr full-path constants and standardizes mod-cache overwrite behavior from GFx snapshots.
• Updates the settings UI to snapshot the cached mod-name list only when the dropdown opens (reducing mutex contention per frame).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/MenuUI.cpp	Updates framework-installed detection caching and snapshots mod dropdown options on open rather than per-frame.
src/MCMNavigator.cpp	Introduces constexpr GFx path constants, overwrites mod cache consistently from GFx, and resets eager Papyrus scheduling on unbound manager.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.