refactor(inbox): derive from snapshot; delete getInbox IPC chain

Sibling refactor to the sidebar-badges cleanup. The inbox aggregates
five item categories (pending approvals, failed runs, budget warnings,
blocked/review tasks, unread company/incident/urgent messages) — every
row is already in `ProfileSnapshot`. The server-side `getInbox`
aggregation (180 lines of SQL + projection) was a redundant second
path.

New: `src/shared/inbox-items.ts::deriveInboxItems(snapshot, companyId)`
produces the same InboxItem[] shape with the same severity ordering
and 24h failed-run window. Pure function, no IPC, no state.

Deleted:
- database/company-crud.ts::getInbox (180-line aggregation)
- database-base.ts::getInbox pass-through
- ipc-core-read-handlers.ts: handler
- preload/index.ts: bridge binding
- shared/contracts/channels.ts: channel name
- shared/contracts/desktop-api/companies.ts: API signature
- state/slices/company.ts: `inboxItems` field, `setInboxItems` action
- useDataLoader.ts: both getInbox call sites (initial snapshot load
  and section-change effect)
- useCompanyController.ts: inbox reset on company switch

OperationsSections now computes `inboxItems` via `useMemo` off the
current snapshot + company id. The snapshot is already company-scoped
at the main/database/snapshot.ts layer when `currentCompanyId` is
non-null; the derivation re-filters defensively so the function works
correctly even for unscoped snapshots.

Tests: 603/603 green. No new tests added — the derivation is a pure
function whose shape is exercised end-to-end by the existing Inbox
component integration.

src/renderer/hooks/useCompanyController.ts

@@ -35,7 +35,6 @@ export function useCompanyController() {
   const clearCompanyScopedUiState = useCallback(() => {
     const store = useAppStore.getState();
     store.clearCompanyScopedSelections();
-    store.setInboxItems([]);
     store.setCompanyMetrics(null);
     store.setStandupReport(null);
     store.setSocialAccounts([]);

src/renderer/hooks/useDataLoader.ts

@@ -24,8 +24,6 @@ export function useDataLoader(
       if (!currentSelectedConnectorId && next.connectors[0]) store.setSelectedConnectorId(next.connectors[0].id);
       if (!currentSelectedRunId && next.runs[0]) store.setSelectedRunId(next.runs[0].id);
       if (next.currentCompanyId) {
-        const inboxResult = await window.agentCompany.getInbox(next.currentCompanyId);
-        if (inboxResult.ok) store.setInboxItems(inboxResult.data);
         store.setSocialAccounts(next.socialAccounts?.filter((a) => a.companyId === next.currentCompanyId) ?? []);
         const browserActionResult = await window.agentCompany.listBrowserActions({ companyId: next.currentCompanyId, limit: 50 });
         if (browserActionResult.ok) {
@@ -50,12 +48,6 @@ export function useDataLoader(
     let cancelled = false;
     const store = useAppStore.getState();
 
-    if (section === "inbox") {
-      void window.agentCompany.getInbox(companyId).then((result) => {
-        if (!cancelled && result.ok) store.setInboxItems(result.data);
-      });
-    }
-
     if (section === "performance") {
       void window.agentCompany.getCompanyMetrics({ companyId, days: 30 }).then((result) => {
         if (!cancelled && result.ok) store.setCompanyMetrics(result.data);