Add a real-browser sheet-metal flange lifecycle regression

[protosphinx]

Why this matters

The repository explicitly says no dedicated real-Chrome sheet-metal lifecycle gate exists. Current tests prove schema and kernel behavior, but not the visible base-flange and edge-flange workflow.

Scope

• Add a small editable sheet-metal profile fixture.
• Drive the existing base-flange and edge-flange dialogs through real mouse and keyboard interaction.
• Verify edit, delete, save and reopen, and exact settlement.
• Keep this issue independent of the currently typed-only corner-relief, bend-table, and flat-pattern dialogs.

Relevant files

• tests/fixtures/sheet-metal-profile.partmode.json
• tests/fixtures/README.md
• scripts/browser-smoke.ts
• docs/sheet-metal.md

Acceptance evidence

• Chrome opens a real project through the visible file boundary.
• The visible dialog creates a base flange and one edge flange.
• Document and kernel revisions settle together with no browser, console, network, or CAD errors.
• Exact B-rep validity, expected analytic volume, and complete topology names are asserted.
• Save and reopen reproduce the same editable records and exact geometry.
• A rejected invalid edit leaves document and applied revisions unchanged.

Test commands

npm run build
npm run smoke:browser
npm run smoke:sheet-metal
npm run smoke:sheet-metal-flat
npm run ci:gate

Contribution size

M: a focused browser fixture and one end-to-end visible lifecycle journey.

Maintainer response expectation

Post the short UI or fixture approach requested above and wait for maintainer scope confirmation before implementation. Review will focus on the listed acceptance evidence.