Project integrity: bind file actions and exports to the active project

[Flow-Fly]

Parent: #337

Problem

Rename and duplicate contain default-context save calls. Export UI and Aseprite writing read singleton stores, so exporting a non-default tab can silently export another drawing.

Scope

• capture the active ProjectContext for rename, duplicate, delete, and update/restart saves
• bind the export dialog to its initiating context
• pass explicit context through PF, PNG/GIF/spritesheet, and Aseprite export paths
• keep compatibility defaults only at safe outer boundaries

Acceptance

• renaming or duplicating tab B saves and copies B, never tab A
• deleting a project clears its own pending save
• every export format reflects the initiating tab
• two-context tests use distinct names, sizes, frames, and pixels