A project-local .vfox.toml entry (e.g. golang = "1.24.0") currently overrides global config even when that version is not installed, which can remove go from PATH inside the workspace. This change keeps scope priority while skipping uninstalled candidates and selecting the highest-priority installed configured version.

• Resolution behavior: prefer installed config by scope order

  • Added shared tool-resolution logic to walk configured versions in priority order (Project -> Session -> Global) and pick the first installed runtime.
  • If a higher-priority scope points to a missing version, resolution now falls through to lower-priority installed versions instead of failing effective tool availability.

• Activation/env pipeline integration

  • Updated activate and env command paths to use installed-aware resolution before symlink/env generation.
  • Existing scope semantics are preserved; only candidate selection changes when configured versions are missing.

• Chain API support for ordered lookup

  • Extended VfoxTomlChain with GetToolConfigsByPriority(name) to return all scope configs for a tool from high to low priority.
  • This avoids ad-hoc lookup duplication and centralizes multi-scope tool selection inputs.

• Targeted coverage

  • Added chain-level test coverage for ordered per-scope config retrieval used by fallback selection.

// high -> low priority, choose first installed
toolConfigs := chain.GetToolConfigsByPriority("golang")
for _, tc := range toolConfigs {
    if sdkObj.CheckRuntimeExist(sdk.Version(tc.Config.Version)) {
        // use tc.Config.Version at tc.Scope
        break
    }
}