Contract: one settings page per repository, the studio's short page on top and the rest beneath #631

Pillar: P1 Feed (umbrella #587). Contract: one of the duplicated screens the studio/dev split left behind. One run, fresh from today's main.

The job: change how a repository or app behaves.

Survivor: one settings page: the studio's short settings first, every other group beneath it on the same page, grouped and quiet.

Removed in this same pull: the split in src/web/pages/settings.ts (ctx.mode === "studio" short shell vs dev's full shell) and "The rest of the settings ?mode=dev" in src/web/studio/crew.ts.

The path: the owner from an app page wants to change one thing; primary action save that group; next back to the app.

Acceptance.

• [ ] One renderer for this job, for every repository and every viewer; the other code and its tests are deleted, not hidden.
• [ ] Every old URL still answers (the survivor, or a redirect); ?mode=dev on it shows the survivor.
• [ ] Nothing the removed screen did is lost: the pull lists each thing it showed or did and where it lives now (or why nobody needs it).
• [ ] Minimal, not bare: one primary next action, white space at every width, nothing the person does not need now.
• [ ] Looks of the path at phone and desktop widths on the pull; the full check green.

Start from: src/web/pages/settings.ts, src/web/studio/crew.ts.

Must not touch: the release workflow, the chart, other repositories.