Add optional activity sorting for sidebar groups

[brsbl]

Human comments

What was wrong

Thread recency only reordered threads inside fixed project, section, and machine lists, leaving active work below older lists.

What changed

• Updated at keeps its select/reverse action; a separate caret opens one optional sorting checkbox.
• The checkbox says Sort projects too, Sort sections too, or Sort machines too, matching the sidebar organization.
• Enabling it extends activity sorting through the hierarchy; disabling it restores saved order. Pinned placement stays fixed.
• Running work remains first and empty lists remain last. The preference is available through the UI, CLI, and SDK.

How you verified

• Remote CI passed checks, all test suites, and package smoke jobs on 8abf42716.
• Chrome for Testing 153.0.8010.36 verified desktop direction toggling and opening the separate caret without changing the sort.
• Phone verification covered the single-option submenu and Back navigation. Remote regression tests cover all three contextual labels.

Before: merge base 2c9fdf2dc. Menu after: exact head 8abf42716. Captures use the same fixture, / route, light theme, viewport, and 2× density. The new submenu's before image shows the preceding sort menu.

Surface · Viewport	Before	After
Sort menu · Desktop · 1280 × 900
Sort menu · Phone · 390 × 844
Updated at submenu · Phone · 390 × 844

Activity-ordering evidence from 91336f5

These ordering captures predate the menu-only revision. Menu evidence above is from the current head.

Surface · Viewport	Before	After
Projects and nested work · Desktop · 1280 × 900
Custom sections · Desktop · 1280 × 900
Machines · Desktop · 1280 × 900

Slop Cop review and P2 follow-ups

Reviewed 25744d61baef359d73926c51a5dec2f4d7debc47 against 8d35c2776bc7fd33f41a64e4c6dd7ebd2f021887 using git diff 8d35c2776..25744d61b. Security and architecture found no issues. Correctness and performance each found one P2. The end-to-end panel accepted the existing exact-build QA evidence. No second review ran.

1. P2 — Keep custom-section membership stable when an environment spans sections. Environment sibling ordering now includes descendants, while section assignment uses the first root. A child becoming active can therefore move a shared environment between its roots' sections without any section ID changing. Root-level activity already exposed this coupling before the PR. Follow up by grouping environments within each root tree's section; verify that activity changes order without changing membership.
2. P2 — Skip section-ranking tree construction when there are no custom sections. Section ID derivation builds a full tree whose result is unused for an empty section list. The rendering child builds that tree separately. This adds work on thread updates, especially with hundreds of retained threads. Follow up with an empty-list return; verify that zero-section mode performs only the rendering build and retains its ordering.

These follow-ups were recorded without expanding this PR. Remaining regression tests cover nested activity, hidden/empty groups, running priority, and sort direction; existing shared tests retain manual and pinned ordering coverage.

BB-Thread-ID: thr_wq5qtf8k3u

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