feat(ui): one-click advisory→blocking ramp control (onboarding)

[JSONbored]

Add the one-action advisory→blocking ramp control (#701 acceptance: 'enables advisory mode in one action'): a single toggle/button on the onboarding surface that flips the repo gate mode via the existing settings mutation. Small control + confirm + optimistic state.

Deliverables

• Ramp control (Switch/StateActionButton) that calls the existing repo gate-mode setter (maintainer-settings.tsx flow)
• AlertDialog confirmation before moving to blocking (components/ui/alert-dialog.tsx)
• Success/failure toast + disabled-while-saving state; reflect current mode from the loaded settings
• Vitest test: advisory→blocking confirm, cancel, and save-failure branches

References

• apps/gittensory-ui/src/components/site/app-panels/maintainer-settings.tsx:287
• apps/gittensory-ui/src/components/ui/alert-dialog.tsx
• apps/gittensory-ui/src/components/site/state-views.tsx:111
• apps/gittensory-ui/src/components/ui/switch.tsx

Part of #701.

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📸 Required: before/after screenshots (this is a UI change)

Non-negotiable. PRs that change UI must include a before/after screenshot table. PRs without it are automatically closed — no exceptions.

Rules:

• Show every page/feature you changed — before and after, one row each.
• Use the markdown table below. Screenshots go inside the table only — no large full-size images pasted elsewhere in the PR.
• Each cell is a clickable thumbnail (a small image linking to the full-size image) with a one-line caption underneath.
• Upload screenshots to the PR by drag-and-drop (GitHub hosts them on its CDN). Do NOT commit image files to the repo.

Copy this and fill it in (replace FULL_IMAGE_URL with the URL GitHub gives you after you drop the image in):

| Page / Feature | Before | After |
|---|---|---|
| `/your-route` | [<img src="FULL_IMAGE_URL" width="260">](FULL_IMAGE_URL)<br><sub>before: short caption</sub> | [<img src="FULL_IMAGE_URL" width="260">](FULL_IMAGE_URL)<br><sub>after: short caption</sub> |

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size: XS · held for later release (gittensor:bug once activated)

[linear-code]

JSO-2319