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/shared/contracts/channels.ts

@@ -35,7 +35,6 @@ export const IPC_CHANNELS = {
   setHeartbeat: "agent-company:set-heartbeat",
   triggerHeartbeat: "agent-company:trigger-heartbeat",
   rendererEvent: "agent-company:event",
-  getInbox: "agent-company:get-inbox",
   getCompanyMetrics: "agent-company:get-company-metrics",
   getStandupReport: "agent-company:get-standup-report",
   bootstrapOnboarding: "agent-company:bootstrap-onboarding",

src/shared/contracts/desktop-api/companies.ts

@@ -1,5 +1,5 @@
 import type { z } from "zod";
-import type { CompanyMetrics, OnboardingBootstrapResult, ProfileSnapshot, StandupReport, InboxItem } from "../../types";
+import type { CompanyMetrics, OnboardingBootstrapResult, ProfileSnapshot, StandupReport } from "../../types";
 import type { bootstrapOnboardingSchema, companyInputSchema, connectorDisabledModelsSchema, connectorInputSchema, settingsSchema } from "../schemas-company";
 import type { metricsQuerySchema } from "../schemas-badges";
 import type { DesktopResult } from "./common";
@@ -18,7 +18,6 @@ export type CompaniesApi = {
   listConnectorModels: (connectorId: string) => Promise<DesktopResult<Array<{ id: string; label: string }>>>;
   getConnectorDisabledModels: (connectorId: string) => Promise<DesktopResult<Array<{ id: string; label: string }>>>;
   setConnectorDisabledModels: (input: z.infer<typeof connectorDisabledModelsSchema>) => Promise<DesktopResult<boolean>>;
-  getInbox: (companyId: string) => Promise<DesktopResult<InboxItem[]>>;
   getCompanyMetrics: (input: z.infer<typeof metricsQuerySchema>) => Promise<DesktopResult<CompanyMetrics>>;
   getStandupReport: (companyId: string) => Promise<DesktopResult<StandupReport>>;
   bootstrapOnboarding: (input: z.infer<typeof bootstrapOnboardingSchema>) => Promise<DesktopResult<OnboardingBootstrapResult>>;