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/preload/index.ts

@@ -43,7 +43,6 @@ const api: DesktopApi = {
   addComment: (input) => ipcRenderer.invoke(IPC_CHANNELS.addComment, input),
   setHeartbeat: (input) => ipcRenderer.invoke(IPC_CHANNELS.setHeartbeat, input),
   triggerHeartbeat: (input) => ipcRenderer.invoke(IPC_CHANNELS.triggerHeartbeat, input),
-  getInbox: (companyId) => ipcRenderer.invoke(IPC_CHANNELS.getInbox, companyId),
   getCompanyMetrics: (input) => ipcRenderer.invoke(IPC_CHANNELS.getCompanyMetrics, input),
   getStandupReport: (companyId) => ipcRenderer.invoke(IPC_CHANNELS.getStandupReport, companyId),
   bootstrapOnboarding: (input) => ipcRenderer.invoke(IPC_CHANNELS.bootstrapOnboarding, input),