Phase 2c — testing infrastructure (43 tests, CI gating, docker-compose)

Brings the project to a TDD/BDD-friendly state — apologies for shipping
Phase 1.5 + Phase 2 code-first, that violated feedback_tdd_first_bdd_required.

What's added :

- helpers_test.go : FakeTelegram (httptest server that records sendMessage /
  deleteMessage / setWebhook / etc.), miniredis bootstrap, MakeUpdate /
  PostWebhook helpers. The same harness simulates 'a user DMing the bot'
  end-to-end without hitting Telegram cloud — answer to the user question.
- 43 tests covering : allowlist parsing, telegram type helpers (UserID /
  ChatID / Text / messageID), secret_token constant-time compare, Backoff
  schedule, Auth (login wrong/right/logout/TTL/nil-receiver), EchoHandler,
  HTTPHandler (forward / timeout / non-2xx / empty body), AuthHandler
  (start / auth / whoami / logout / replay defense delete), Server (bad
  secret 401, unknown bot 404, allowlist drop, gated bot prompt,
  full /auth → echo → /logout flow, healthz/readyz).
- All tests pass with -race in 1.6s, no external deps (miniredis +
  httptest in-process).

Infra :

- Updated .gitea/workflows/dockerimage.yaml : new 'test' job
  (go vet + go test -race) gates the build-and-push-image job. CI now
  also runs on pull_request.
- docker-compose.yml : redis + postgres for full local stack.
- Makefile : test-race, compose-up/down targets.
- README updated with test + local-dev sections.

Refs ~/.claude/plans/pour-les-notifications-on-inherited-seal.md § Phase 2.

go.mod

@@ -3,6 +3,7 @@ module github.com/arcodange/telegram-gateway
 go 1.24
 
 require (
+	github.com/alicebob/miniredis/v2 v2.37.0
 	github.com/lib/pq v1.12.3
 	github.com/redis/go-redis/v9 v9.19.0
 	gopkg.in/yaml.v3 v3.0.1
@@ -10,5 +11,8 @@ require (
 
 require (
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/stretchr/testify v1.8.2 // indirect
+	github.com/yuin/gopher-lua v1.1.1 // indirect
 	go.uber.org/atomic v1.11.0 // indirect
+	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
 )