Promote AgentCompany-New to the repository root and retire the old app

The legacy application - its src, tests, landing site, promo assets, docs,
release tooling, CI workflows, and root configs - leaves the tree; it stays
reachable in history. Everything under AgentCompany-New moves up unchanged:
same package name, so the production userData/database path is untouched,
and e2e/build scripts already resolved paths relative to the project. The
developer cred.txt stays gitignored at its new location. Full verify:ci
passes from the new root.

src/main/services/provider-adapter-contract.ts

@@ -0,0 +1,75 @@
+import type { ProviderAuthType } from "../../shared/domain";
+import type { ProviderModelEntry } from "../../shared/provider-models";
+import type { ProviderObservedRateLimitState } from "../../shared/provider-runtime-domain";
+import type { ProviderAuthProfile } from "./provider-auth-profiles";
+import type { ProviderBackgroundCreateResult, ProviderBackgroundRetrieveResult } from "./provider-background";
+import type { ProviderAuthorizeHandler, ProviderRefreshHandler, ProviderRevokeHandler } from "./provider-auth-lifecycle";
+import type { ProviderCancelResult, ProviderStreamResult } from "./provider-streaming";
+
+export interface ProviderExecutionInput {
+  authProfile: ProviderAuthProfile;
+  model: string;
+  prompt: string;
+  instructions: string | null;
+}
+
+export interface ProviderExecutionResult {
+  text: string;
+  rawResponseJson: string;
+  rateLimitState: ProviderObservedRateLimitState | null;
+}
+
+export type ProviderStreamInput = ProviderExecutionInput;
+export type ProviderBackgroundCreateInput = ProviderExecutionInput;
+
+export interface ProviderCancelInput {
+  authProfile: ProviderAuthProfile;
+  responseId: string;
+}
+
+export interface ProviderBackgroundRetrieveInput {
+  authProfile: ProviderAuthProfile;
+  responseId: string;
+}
+
+export interface ProviderHealthInput {
+  authProfile: ProviderAuthProfile;
+  model: string | null;
+}
+
+export interface ProviderHealthResult {
+  checkedAt: string;
+  rateLimitState: ProviderObservedRateLimitState | null;
+}
+
+export interface ProviderContext {
+  authProfile: ProviderAuthProfile;
+  model: string | null;
+}
+
+export interface ProviderRateLimitState {
+  requestLimit: number | null;
+  remainingRequests: number | null;
+  resetAt: string | null;
+  retryAfterMs: number | null;
+  rawStateJson: string;
+}
+
+export interface ProviderAdapter {
+  providerKey: string;
+  authType: ProviderAuthType;
+  authorize: ProviderAuthorizeHandler;
+  refresh: ProviderRefreshHandler;
+  revoke: ProviderRevokeHandler;
+  parseAuthProfile(secret: string): ProviderAuthProfile;
+  listModels(ctx: ProviderContext): Promise<ProviderModelEntry[]>;
+  getRateLimitState(ctx: ProviderContext): Promise<ProviderRateLimitState | null>;
+  checkHealth(input: ProviderHealthInput): Promise<ProviderHealthResult>;
+  streamResponse(input: ProviderStreamInput): Promise<ProviderStreamResult>;
+  cancelResponse(input: ProviderCancelInput): Promise<ProviderCancelResult>;
+  createBackgroundResponse(input: ProviderBackgroundCreateInput): Promise<ProviderBackgroundCreateResult>;
+  retrieveResponse(input: ProviderBackgroundRetrieveInput): Promise<ProviderBackgroundRetrieveResult>;
+  createResponse?: (input: ProviderExecutionInput) => Promise<ProviderExecutionResult>;
+}
+
+export type ProviderAdapterRegistry = Record<string, ProviderAdapter>;