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/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";