Clarify Text Edit empty states and path hints

[baseGame]

Summary

First-time Text Edit users hit confusing empty-state and path gaps:

• No empty-pane guidance beyond a faint editor placeholder; unclear it is a single-file editor (not Text Compare).
• Path field had no file-path placeholder; Enter did nothing.
• Open stayed tip-less when disabled for a missing path.
• Open/save errors were raw String(error) dumps.
• Path footer format said jargon Everything Else.

Changes

• Stage-aware empty hint (choose file → press Enter / Open).
• File-path placeholder; Enter opens the file when a path is set.
• Clearer Open tooltip when no path is chosen.
• Route open/save errors through formatCompareError.
• Path footer format label Text; clearer editor placeholder.

Test plan

• TextEditView unit tests (empty / Enter)
• Prettier / ESLint / Stylelint / vue-tsc (pre-commit quality)
• CI green