Add Trip Editor error-state contract coverage

[stef-k]

Summary

Implements #297 Batch 3 only: Trip Editor stale/error/dirty/delete feedback contracts.

• Adds focused mocked Playwright coverage for failure feedback and state preservation.
• Failed place save keeps the active draft and leaves persisted row/API state unchanged.
• Failed segment save covers the separate SegmentManager feedback path and keeps draft values.
• Delete confirmation gates mutation; canceled confirmation sends no request.
• Failed delete keeps the editor/row visible and shows danger feedback.
• Clean cancel and dirty keep/discard paths behave deterministically.

Claim Boundary

These tests intentionally use mocked non-2xx mutation responses for hard-to-trigger browser failure states. They prove frontend failure feedback and state preservation only. They do not claim CRUD persistence proof.

Batch 2 real endpoint specs cover successful delete/removal/persistence. This PR does not duplicate that success proof.

Out Of Scope

• Batch 4 search-add real persistence after Trip Editor RC geosearch add-place workflow and place-edit parity regressions #295.
• Batch 5 rich-notes sanitizer/persistence real contract.
• Batch 6 Development/published production asset smoke.
• Product behavior changes.

Validation

• Focused new spec: 4 passed.
• Playwright list: passed, 114 tests listed.
• dotnet build: passed.
• dotnet test: passed, 1537 tests.
• LOC check: passed; no new Batch 3 warning.
• git diff --check origin/main...HEAD: passed.
• tracked artifact scan: clean.