refactor: centralize types and extract seed data (Task 1.1)

- Create types/ directory with centralized domain types:
  session, tool-instance, tool-type, git-repository, config-folder,
  tool-config, project, user, api-response
- Remove inline type definitions from API modules;
  re-export from types/ for backward compatibility
- Update state/sessions.tsx to import Session from types/session.ts
- Update all consumer components/pages to import from types/
- Extract seed_builtin_tool_types from main.py to
  seeds/builtin_tool_types.py
- Create types/index.ts barrel export

Quality gates: tsc (pass), eslint (pass), Python syntax (pass)

apps/web/src/components/app-shell.tsx

@@ -2,7 +2,7 @@ import { useCallback, useEffect } from "react";
 import { Link, NavLink, Outlet } from "react-router-dom";
 
 import { getUserSessions } from "../api/sessions";
-import type { Session } from "../api/sessions";
+import type { Session } from "../types/session";
 import { useTheme } from "../hooks/use-theme";
 import { useAuth } from "../state/auth";
 import { useSessions } from "../state/sessions";

apps/web/src/components/instance-list.tsx

@@ -1,7 +1,8 @@
 import { useCallback, useEffect, useState } from "react";
 import { useNavigate } from "react-router-dom";
 import { Icon } from "./icon";
-import type { ToolInstance } from "../api/sessions";
+import type { ToolInstance } from "../types/tool-instance";
+import type { ToolType } from "../types/tool-type";
 import {
   checkInstanceHealth,
   createInstance,
@@ -12,7 +13,6 @@ import {
   startInstance,
   stopInstance,
 } from "../api/sessions";
-import type { ToolType } from "../api/tool_types";
 
 const API_BASE_URL = import.meta.env.VITE_API_BASE_URL ?? "http://localhost:8000";
 

apps/web/src/components/repositories-settings-tab.tsx

@@ -1,7 +1,8 @@
 import React, { useCallback, useEffect, useState } from "react";
 import { useParams } from "react-router-dom";
 
-import { deleteRepository, listRepositories, type GitRepository } from "../api/git_repositories";
+import type { GitRepository } from "../types/git-repository";
+import { deleteRepository, listRepositories } from "../api/git_repositories";
 import { RepositoryCreateDialog } from "./repository-create-dialog";
 import { Icon } from "./icon";
 

apps/web/src/components/repository-create-dialog.tsx

@@ -1,6 +1,7 @@
 import { useEffect, useRef, useState } from "react";
 
-import { createRepository, parseGitUrl, type GitRepositoryCreate, type URLParseResult } from "../api/git_repositories";
+import type { GitRepositoryCreate, URLParseResult } from "../types/git-repository";
+import { createRepository, parseGitUrl } from "../api/git_repositories";
 import { Icon } from "./icon";
 
 type CreateMode = "clone" | "blank";