feat(frontend): persist sidebar panel layout across browser refreshes via localStorage

Carries the in-app sidebar layout (which views are open and in what
order) across page reloads. Closes the natural follow-up to the tab-
restore feature in d2e2e67: tabs survive, but until now the sidebar
panels (Chat Settings / Tasks / Skills / Tools / etc.) reset to a
single default panel on every load.

Scope (explicitly bounded by the user):
  - Persistence target: localStorage. Matches the precedent for UI
    preferences (`dispatch-theme`, `dispatch-api-url`). Per-device
    layout; no backend round-trip.
  - sidebarOpen (the Header button that hides the whole sidebar
    column) is NOT persisted; always starts open on every load.
  - No drag-to-reorder UI added — persistence captures whatever order
    the user established via the existing add/remove buttons.

Implementation:

  • New `packages/frontend/src/lib/sidebar-storage.ts` — pure
    functions `loadSidebarPanels(): string[]` and
    `saveSidebarPanels(selected: string[]): void`. localStorage key
    is `dispatch-sidebar-panels` (canonical `dispatch-` prefix).
    `loadSidebarPanels` is defensive against every failure mode
    (missing key, malformed JSON, non-array root, non-string entries,
    empty-after-filter, localStorage.getItem throwing under
    SecurityError). Returns a fresh array on every call so mutations
    by the caller don't pollute the module-level default constant.
    `saveSidebarPanels` swallows storage errors (quota / disabled /
    SecurityError) — best-effort.

  • `packages/frontend/src/lib/components/SidebarPanel.svelte`:
    seed the `panels: $state` from `loadSidebarPanels().map(s => ({
    id: nextId++, selected: s }))` and add a `$effect` that calls
    `saveSidebarPanels(panels.map(p => p.selected))` whenever
    `panels` changes. The session-ephemeral `id` field is regenerated
    on every mount; only the `selected` strings round-trip.

  • Existing addPanel / remove / dropdown handlers untouched — they
    all reassign `panels` (`panels = [...panels, ...]`,
    `panels = panels.filter(...)`, `panels = panels.map(...)`),
    which triggers the new $effect. The minimum-one-panel invariant
    (X button hidden on idx 0) is preserved at the UI layer and
    reinforced by the loader's empty-fallback to the default layout.

Tests: 15 new in `packages/frontend/tests/sidebar-storage.test.ts` —
load with empty / valid / malformed / non-array / null / mixed-type /
empty-after-filter / throwing-getItem; save round-trip; save error
swallowing; overwrite semantics; empty-save / load-fallback; mutation
isolation.

Frontend total: 59 tests (was 44; +15). API 31, core 168 unchanged.
Typecheck clean (svelte-check 0 errors), biome clean (126 files).

Gemini code review (yolo mode, prompt-level write restriction to
report.md only): SHIP, no findings.

0 files changed, 0 insertions, 0 deletions