fix(docs): correct error codes and coach list reference (#557)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: nanotaboada

README.md

@@ -124,7 +124,7 @@ Interactive API documentation is available via Swagger UI at `http://localhost:9
 | `DELETE` | `/players/squadnumber/{squad_number}` | Remove player by squad number | `204 No Content` |
 | `GET` | `/health` | Health check | `200 OK` |
 
-Error codes: `400 Bad Request` (validation failed) · `404 Not Found` (player not found) · `409 Conflict` (duplicate squad number on `POST`)
+Error codes: `400 Bad Request` (squad number mismatch on `PUT`) · `404 Not Found` (player not found) · `409 Conflict` (duplicate squad number on `POST`) · `422 Unprocessable Entity` (schema validation failed)
 
 For complete endpoint documentation with request/response schemas, explore the [interactive Swagger UI](http://localhost:9000/docs).
 

RELEASES.md

@@ -36,7 +36,7 @@ Before creating the tag, verify all of the following:
 - [ ] `CHANGELOG.md` `[Unreleased]` section is moved to a new versioned release entry
 - [ ] Release PR is merged into `master`
 - [ ] `uv run pytest` passes
-- [ ] Coach name is valid and follows alphabetical order (see [famous coach list](CHANGELOG.md))
+- [ ] Coach name is valid and follows alphabetical order (see "Release Naming Convention" in [CHANGELOG.md](CHANGELOG.md))
 - [ ] All CI checks on `master` are green
 
 ### 4. Create and Push Tag