feat(sproutclaw): modularize webui, extensions, and agent config layout

Restructure local extensions into per-feature directories, split WebUI
into backend modules with slash commands and systemd support, and track
prompts/skills under .pi/agent for portable Gitea deployment.

Co-authored-by: Cursor <cursoragent@cursor.com>

.pi/agent/extensions/webui/backend/config/paths.ts

@@ -0,0 +1,56 @@
+import { existsSync } from "node:fs";
+import { dirname, join, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const configDir = dirname(fileURLToPath(import.meta.url));
+const backendDir = dirname(configDir);
+const extensionRoot = resolve(backendDir, "..");
+
+export interface WebUiPaths {
+	extensionRoot: string;
+	repoRoot: string;
+	agentDir: string;
+	publicDir: string;
+	pidFile: string;
+	sessionsDir: string;
+	agentExtensionsDir: string;
+	agentNpmNodeModules: string;
+	agentSettingsFile: string;
+	systemPromptFile: string;
+	modelsConfigFile: string;
+	mcpCacheFile: string;
+	mcpConfigFile: string;
+	piCliDist: string;
+}
+
+export function createWebUiPaths(): WebUiPaths {
+	const repoRoot = process.cwd();
+	const agentDir = resolve(process.env.PI_CODING_AGENT_DIR || join(repoRoot, ".pi", "agent"));
+
+	return {
+		extensionRoot,
+		repoRoot,
+		agentDir,
+		publicDir: join(extensionRoot, "frontend", "dist"),
+		pidFile: join(extensionRoot, ".webui.pid"),
+		sessionsDir: join(agentDir, "sessions"),
+		agentExtensionsDir: join(agentDir, "extensions"),
+		agentNpmNodeModules: join(agentDir, "npm", "node_modules"),
+		agentSettingsFile: join(agentDir, "settings.json"),
+		systemPromptFile: join(agentDir, "AGENTS.md"),
+		modelsConfigFile: join(agentDir, "models.json"),
+		mcpCacheFile: join(agentDir, "mcp-cache.json"),
+		mcpConfigFile: join(agentDir, "mcp.json"),
+		piCliDist: join(repoRoot, "packages", "coding-agent", "dist", "cli.js"),
+	};
+}
+
+export function resolvePiRpcLaunch(paths: WebUiPaths): { command: string; args: string[]; mode: "dist" } {
+	const rpcArgs = ["--mode", "rpc"];
+	if (!existsSync(paths.piCliDist)) {
+		throw new Error(
+			`[webui] 构建版 sproutclaw 未找到: ${paths.piCliDist}。请先运行: sproutclaw build`,
+		);
+	}
+	return { command: process.execPath, args: [paths.piCliDist, ...rpcArgs], mode: "dist" };
+}