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-tool-turn.ts

@@ -0,0 +1,76 @@
+/**
+ * Shared contract for a single tool-use ("function calling") turn against any
+ * provider backend. The agent loop maintains a normalized conversation
+ * ({@link AgentTurnMessage}[]) plus the requested {@link ToolDefinition}s; each
+ * provider's turn function (under `provider-tool-turns/`) translates that into
+ * the backend's wire format, calls the live endpoint, and parses the reply plus
+ * any tool calls back into {@link AgentTurnResult}.
+ */
+import { isRecord, type JsonRecord } from "./provider-http";
+
+export interface ToolDefinition {
+  name: string;
+  description: string;
+  /** JSON Schema for the tool's arguments. */
+  parameters: JsonRecord;
+}
+
+export interface ToolCall {
+  id: string;
+  name: string;
+  arguments: JsonRecord;
+}
+
+export type AgentTurnMessage =
+  | { role: "user"; text: string }
+  | { role: "assistant"; text: string; toolCalls: ToolCall[] }
+  | { role: "tool"; results: Array<{ toolCallId: string; toolName: string; output: string }> };
+
+export interface AgentTurnResult {
+  text: string;
+  toolCalls: ToolCall[];
+  rawResponseJson: string;
+}
+
+/** Resolved per-request credential, already refreshed if it was an OAuth token. */
+export interface TurnCredential {
+  apiKey?: string;
+  accessToken?: string;
+  accountId?: string;
+  projectId?: string;
+  enterpriseUrl?: string | null;
+  /** Base URL for Azure and custom OpenAI/Anthropic-compatible endpoints. */
+  baseUrl?: string;
+  deployment?: string;
+  /** AWS Bedrock. */
+  region?: string;
+  accessKeyId?: string;
+  secretAccessKey?: string;
+  sessionToken?: string | null;
+  /** Vertex AI service-account JSON. */
+  serviceAccountJson?: string;
+}
+
+export interface ProviderToolTurnInput {
+  credential: TurnCredential;
+  model: string;
+  instructions: string | null;
+  messages: AgentTurnMessage[];
+  tools: ToolDefinition[];
+}
+
+export type ToolTurnFn = (input: ProviderToolTurnInput) => Promise<AgentTurnResult>;
+
+/** Coerce a tool-call argument payload (string or object) into a JSON object. */
+export function parseArguments(value: unknown): JsonRecord {
+  if (isRecord(value)) return value;
+  if (typeof value === "string" && value.trim()) {
+    try {
+      const parsed = JSON.parse(value) as unknown;
+      if (isRecord(parsed)) return parsed;
+    } catch {
+      return {};
+    }
+  }
+  return {};
+}