Add TanStack Start stack detection

[CarlosZiegler]

Summary

Adds first-class TanStack Start support to Openship's stack registry and GitHub import detection.

This keeps TanStack Start projects from being detected as plain Vite apps, so they get fullstack defaults instead of static Vite defaults.

Changes

• Add a tanstack-start stack with .output server output, port 3000, and node .output/server/index.mjs as the default start command
• Detect TanStack Start before generic Vite detection
• Support common Vite, Rsbuild, and older app.config.* project markers when paired with TanStack Start dependencies
• Add regression tests for TanStack Start vs plain Vite detection

Closes #400.

Verification

• bun --filter @repo/api test -- test/lib/stack-detector.test.ts
• bun --filter @repo/core test
• bun --filter @repo/api lint
• bun --filter @repo/core lint
• git diff --check