2.5.8 The `[Tree ▾]` view-switcher — Tree ↔ flat sortable List (URL-driven)

Estimate: 16m · Depends on: 2.5.3, 2.5.7

Make the [Tree ▾] control in the 2.5.3 toolbar FUNCTIONAL: a real menu (Popover/Combobox) toggling between the existing Tree view and a new flat, sortable List view, per 2.5.7's design. The 2.5.3 toolbar ships the control disabled as a forward-compatible seam; this replaces that placeholder with the working switcher.

Durable shape: view + sort live in the URL (e.g. ?view=list&sort=key:asc), exactly like 2.5.4's filter params — shareable / reload-safe and the same serialization Epic 6's saved views will persist. The Server Component reads them: view=tree (default) renders the nested TreeTable (2.5.2); view=list renders a flat table (the project's issues un-nested, sorted by the active key) reusing the same row cells. List sorting is a flat ORDER BY over the existing project read — add a flat, sorted variant of 2.5.1's read; do NOT re-nest then flatten in JS.

Scope guard. v1 = the Tree/List toggle + single-column sort with the drawn affordance. Saved / named views, multi-sort, and column show/hide config stay Epic 6 (saved views & advanced search) — not invented here (no complexity for nothing).

Acceptance criteria

• The [Tree ▾] control opens a menu with Tree (default) + List; choosing one switches the view and reflects the choice in the URL (?view=), reload-/share-safe.
• List renders the project's issues FLAT, sorted by the active column; clicking a sortable header updates ?sort= (asc/desc) with the drawn active-sort indicator; default sort = key asc.
• Both views reuse the same row cells + the whole-row link to /issues/[key]; matches list.mock.html (2.5.7); colours via --el-*, status via Pill tones.
• 4-layer + explicit workspace gate; the flat read reuses/extends 2.5.1 (no N+1, no JS re-nesting).
• Component test (toggle view + sort updates the URL + re-queries). The Tree↔List switch + sort round-trip is driven end-to-end by the Story E2E (2.5.6), which also adds the List view to the strict shell-a11y sweep — so the sortable headers must carry aria-sort.

Context refs

• design/work-items/list.mock.html + design-notes.md (2.5.7) — the layout authority
• 2.5.3 app/(authed)/issues/page.tsx + _components/IssueListToolbar (the disabled [Tree ▾] to wire) + IssueTreeTable / issueRows
• 2.5.1 getProjectTree / findProjectForest (add the flat, sorted variant); 2.5.4's URL-param pattern; components/ui/Popover / Combobox
• motir-core/CLAUDE.md — 4-layer · --el-* tokens