feat(sdk): use config file as single source of truth, remove env var fallbacks (#19409)

## Summary

- **Config as source of truth**: `~/.twenty/config.json` is now the
single source of truth for SDK authentication — env var fallbacks have
been removed from the config resolution chain.
- **Test instance support**: `twenty server start --test` spins up a
dedicated Docker instance on port 2021 with its own config
(`config.test.json`), so integration tests don't interfere with the dev
environment.
- **API key auth for marketplace**: Removed `UserAuthGuard` from
`MarketplaceResolver` so API key tokens (workspace-scoped) can call
`installMarketplaceApp`.
- **CI for example apps**: Added monorepo CI workflows for `hello-world`
and `postcard` example apps to catch regressions.
- **Simplified CI**: All `ci-create-app-e2e` and example app workflows
now use a shared `spawn-twenty-app-dev-test` action (Docker-based)
instead of building the server from source. Consolidated auth env vars
to `TWENTY_API_URL` + `TWENTY_API_KEY`.
- **Template publishing fix**: `create-twenty-app` template now
correctly preserves `.github/` and `.gitignore` through npm publish
(stored without leading dot, renamed after copy).

## Test plan

- [x] CI SDK (lint, typecheck, unit, integration, e2e) — all green
- [x] CI Example App Hello World — green
- [x] CI Example App Postcard — green
- [x] CI Create App E2E minimal — green
- [x] CI Front, CI Server, CI Shared — green

.github/workflows/ci-sdk.yaml

@@ -70,6 +70,8 @@ jobs:
           - 6379:6379
     env:
       NODE_ENV: test
+      TWENTY_API_URL: http://localhost:3000
+      TWENTY_API_KEY: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIyMDIwMjAyMC1lNmI1LTQ2ODAtOGEzMi1iODIwOTczNzE1NmIiLCJ1c2VySWQiOiIyMDIwMjAyMC1lNmI1LTQ2ODAtOGEzMi1iODIwOTczNzE1NmIiLCJ3b3Jrc3BhY2VJZCI6IjIwMjAyMDIwLTFjMjUtNGQwMi1iZjI1LTZhZWNjZjdlYTQxOSIsIndvcmtzcGFjZU1lbWJlcklkIjoiMjAyMDIwMjAtNDYzZi00MzViLTgyOGMtMTA3ZTAwN2EyNzExIiwidXNlcldvcmtzcGFjZUlkIjoiMjAyMDIwMjAtMWU3Yy00M2Q5LWE1ZGItNjg1YjUwNjlkODE2IiwidHlwZSI6IkFDQ0VTUyIsImF1dGhQcm92aWRlciI6InBhc3N3b3JkIiwiaWF0IjoxNzUxMjgxNzA0LCJleHAiOjIwNjY4NTc3MDR9.HMGqCsVlOAPVUBhKSGlD1X86VoHKt4LIUtET3CGIdik
     steps:
       - name: Fetch custom Github Actions and base branch history
         uses: actions/checkout@v4