Align background-agent picker with Settings

[hamzamerzic]

Summary

• replace the split inherit/override controls with the same full-width model picker pattern used by Möbius Settings
• wrap those choices in Settings-style draggable priority rows; pointer drag or keyboard arrows swaps primary and fallback
• show “Default from settings” as the selected inherited row and switch to an app override when a model is chosen
• keep News’ immediate durable-save, newest-wins, and rollback behavior
• show effort as accessible Settings-style dots and expose selected rows to assistive technology
• release News 1.14.11

Validation

• npm test — 84/84 passed
• platform validate-app.py — 0 errors, 0 warnings
• git diff --check

[hamzamerzic]

Independent exact-head review (fef458b422f608d88c288005eb82d301f867edb0): hold merge pending two fixes.

1. ModelPicker renders its position:absolute; inset:0 backdrop inside .mobius-agent-priority-row (a positioned/transform stacking context). The backdrop is row-bounded and the sheet cannot reliably cover/dismiss across the app. Clean production already contains the missing follow-up: portal the sheet to document.body (1c3aa0f, with regression test 59e0dad). Please bring that fix here while retaining this PR's stronger triggerLabel and aria-pressed semantics.

2. The reorder is not identity-preserving when either row inherits Settings. primary_agent_mode: system resolves system choice 0, while secondary_agent_mode: system resolves system choice 1. Example: [system primary A, app override C] is swapped by the UI into [app C, system secondary B], not [C, A]; [system A, system B] is a no-op. Because News persists the swap immediately, this can durably save a different agent set than the drag preview promises. Either materialize the resolved inherited choices when reordering, add a stable source/order contract, or disable/clarify reorder for inherited rows.

Follow-up quality: the drag handles are named only by ordinal (Move background agent priority 1/2), unlike Settings' provider-named handles, and there is no reorder announcement. Please include agent identity and an aria-live result if this remains draggable.

Verified: exact head is clean/mergeable with green CI; npm test 84/84; current platform validate-app.py 0 errors/0 warnings; manifest/version/source-file/bundle closure and git diff --check pass. News' immediate durable-write, superseded-response guard, rollback, and same-agent warning remain intact.

[hamzamerzic]

Post-merge exact-head closure: I rechecked final 517b7ced97fc38a511de701219f3ceb4baa9fad7 after the requested fixes. The picker is body-portaled; inherited rows cannot perform identity-changing reorder; and drag handles/live announcements identify the affected agents. News still preserves its immediate durable-write, superseded-response, rollback, and same-agent warning contracts. Final validation: 85 tests passed. The earlier hold is fully resolved.