feat(admin): generate review config from dashboard controls

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Summary

Plan and implement a dashboard/admin UI that lets self-hosters and repo maintainers select review configuration visually and generate valid config from those choices.

Context

Editing YAML by hand is acceptable for maintainers, but the long-term self-host experience should expose the supported provider, review, REES, and analyzer options through a dashboard. This should build on a real config schema rather than duplicating rules in the UI.

Requirements

• Depend on the complete/minimal config template work and any schema/validator changes.
• Expose provider selection, model/effort options, review mode, REES analyzer toggles, and supported review behavior controls.
• Show defaults and invalid combinations clearly.
• Generate config that can be copied or applied without secrets embedded.
• Preserve advanced file-based configuration for operators who prefer it.

Deliverables

• UI plan for config controls and generated output.
• Schema-backed validation path shared with runtime config where practical.
• Generated config preview.
• Tests for valid, invalid, and default selections.
• Documentation explaining dashboard-generated config versus manual config.

Acceptance criteria

• Generated config validates with the same rules used by the review runtime.
• The UI does not expose or store provider secrets accidentally.
• Manual config remains supported and documented.