docs: require Linear issues and auto-ship PRs (#4)

## WHAT

- `AGENTS.md` e `docs/agents/issue-tracker.md`: todo trabalho e todo PR precisam de issue Linear.
- SDLC automático: trabalho feito → testes feitos ou atualizados → pre-commit verde → commit → PR, sem perguntar.
- Templates de PR idênticos no Gitea (`.gitea/PULL_REQUEST_TEMPLATE.md`) e no GitHub (`.github/pull_request_template.md`) com WHAT / WHY / HOW / Linear Issue / Comments.

## WHY

Agentes estavam soltos no tracker e paravam pra perguntar se podiam commitar. O contrato precisa ser o ciclo completo, com issue Linear e template de PR.

## HOW

Docs e templates only. Sem mudança de runtime. Pre-commit (`composer pint:check` + `composer phpstan`) passou.

## Linear Issue

- [MAN-132](https://linear.app/maneco-workspace/issue/MAN-132/exigir-issue-linear-em-todo-trabalho-e-pr)
- [MAN-133](https://linear.app/maneco-workspace/issue/MAN-133/adicionar-pr-template-no-gitea-e-no-github)

## Comments

GitHub é o mirror legado; o PR canônico é este no Gitea.

Reviewed-on: #4
Co-authored-by: manoel freitas <manoel.josefneto@gmail.com>
Co-committed-by: manoel freitas <manoel.josefneto@gmail.com>

.gitea/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,19 @@
+## WHAT
+
+<!-- What changed? -->
+
+## WHY
+
+<!-- Why this change? -->
+
+## HOW
+
+<!-- How was it implemented? Include verification. -->
+
+## Linear Issue
+
+<!-- Required. Identifier + URL, e.g. MAN-133 https://linear.app/maneco-workspace/issue/MAN-133 -->
+
+## Comments
+
+<!-- Notes for reviewers. Screenshots, follow-ups, out of scope. -->