feat: M7 proper LLM integration with dual providers, caching, and parallel batching

- Add LLM client abstraction (src/llm-client.ts) with factory pattern
- Add OpenAI-compatible external client (src/external-llm-client.ts)
- Add Kimi.com client using Anthropic-based API (src/kimi-llm-client.ts)
- Add Pi native LLM stub (src/pi-llm-client.ts) for future ExtensionAPI wiring
- Add SHA-256 disk cache at ~/.cache/pi-project-map/ (src/llm-cache.ts)
- Add parallel batching with p-limit, retry + exponential backoff (src/llm-batch.ts)
- Rewrite llm-extract.ts to use real LLM calls with structured prompts
  - File-level: PURPOSE, DEPS, CONCEPTS
  - Package-level: ROLE, ARCH
  - Context truncation, 50KB skip, cache before LLM call
- Wire CLI with --llm-provider, --llm-model, --llm-base-url flags
- Update config.ts with llmProvider, llmBaseUrl fields
- Update init.ts and patch.ts to accept optional LLMClient
- Add sample project fixture for manual testing
- Add tests: llm-cache (3), llm-batch (5), llm-integration (8 with real Kimi API),
  pi-extension (14 mocked)
- All 56 tests pass

fixtures/sample-project/tests/user.test.ts

@@ -0,0 +1,24 @@
+import { describe, it, expect } from "vitest";
+import { createUser, serializeUser } from "../src/models/user.js";
+
+describe("User model", () => {
+  it("creates a user with valid email", () => {
+    const user = createUser({ email: "alice@example.com", name: "Alice" });
+    expect(user.email).toBe("alice@example.com");
+    expect(user.name).toBe("Alice");
+    expect(user.id).toBeDefined();
+    expect(user.createdAt).toBeInstanceOf(Date);
+  });
+
+  it("throws on invalid email", () => {
+    expect(() =>
+      createUser({ email: "not-an-email", name: "Bob" }),
+    ).toThrow("Invalid email");
+  });
+
+  it("serializes to JSON", () => {
+    const user = createUser({ email: "charlie@example.com", name: "Charlie" });
+    const json = serializeUser(user);
+    expect(JSON.parse(json).name).toBe("Charlie");
+  });
+});

fixtures/sample-project/tests/validation.test.ts

@@ -0,0 +1,21 @@
+import { describe, it, expect } from "vitest";
+import { validateEmail, validateNotEmpty, validateMinLength } from "../src/utils/validation.js";
+
+describe("Validation utils", () => {
+  it("validates email format", () => {
+    expect(validateEmail("test@example.com")).toBe(true);
+    expect(validateEmail("invalid")).toBe(false);
+    expect(validateEmail("")).toBe(false);
+  });
+
+  it("checks non-empty strings", () => {
+    expect(validateNotEmpty("hello")).toBe(true);
+    expect(validateNotEmpty("   ")).toBe(false);
+    expect(validateNotEmpty("")).toBe(false);
+  });
+
+  it("checks minimum length", () => {
+    expect(validateMinLength("hello", 3)).toBe(true);
+    expect(validateMinLength("hi", 3)).toBe(false);
+  });
+});