feat: move LLM cache to project-local directory

- Cache now lives in <project>/.pi-project-map/cache/llm-cache.json
- Removed global ~/.cache/pi-project-map/ usage
- Cache travels with the project, no cross-project collisions
- Easy to invalidate: rm -rf .pi-project-map/cache/

Files changed:
- llm-cache.ts: accept cacheDir parameter, default to project-local
- llm-extract.ts: pass cacheDir through to cache functions
- init.ts: pass rootPath as cacheDir
- patch.ts: accept and pass cacheDir
- cli.ts: pass targetPath as cacheDir
- pi-extension.ts: pass ctx.cwd as cacheDir
- Tests updated to use temp dirs for cache isolation

pi-extension.ts

@@ -2,7 +2,12 @@ import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
 import { Type } from "typebox";
 import { readFileSync, readdirSync, statSync } from "fs";
 import { join, relative } from "path";
-import { initProject, patchFile, validateMaps, reinitPath } from "./src/index.js";
+import {
+	initProject,
+	patchFile,
+	validateMaps,
+	reinitPath,
+} from "./src/index.js";
 import { createLLMClient } from "./src/llm-client.js";
 import { LLMError } from "./src/llm-error.js";
 
@@ -73,7 +78,7 @@ export default function (pi: ExtensionAPI) {
 			try {
 				const targetPath = params.path || ctx.cwd;
 				const client = getPiLLMClient(ctx);
-				await initProject(targetPath, { verbose: false, llmClient: client });
+				await initProject(targetPath, { verbose: false, llmClient: client, cacheDir: ctx.cwd });
 				return {
 					content: [
 						{
@@ -111,7 +116,7 @@ export default function (pi: ExtensionAPI) {
 		async execute(_toolCallId, params, _signal, _onUpdate, ctx) {
 			try {
 				const client = getPiLLMClient(ctx);
-				await patchFile(params.file_path, client);
+				await patchFile(params.file_path, client, ctx.cwd);
 				return {
 					content: [
 						{
@@ -194,7 +199,7 @@ export default function (pi: ExtensionAPI) {
 			try {
 				const targetPath = params.path || ctx.cwd;
 				const client = getPiLLMClient(ctx);
-				await reinitPath(targetPath, { verbose: false, llmClient: client });
+				await reinitPath(targetPath, { verbose: false, llmClient: client, cacheDir: ctx.cwd });
 				return {
 					content: [
 						{