docs: add AGENTS.md and CONTRIBUTING.md (GRO-2381)

Point at the authoritative groombook/org skills (sdlc, coding-standards,
safety) and document the phase-by-phase PR flow + uat->main merge-gate
policy summary. Whitelist reminder for main branch protection: engineer
team only.

cc @cpfarhood

Co-Authored-By: Paperclip <noreply@paperclip.ing>

AGENTS.md

@@ -0,0 +1,54 @@
+# AGENTS.md
+
+This repository (`groombook/api`) is part of the GroomBook application stack. The
+authoritative process, quality bar, and safety rules live in the shared
+[`groombook/org`](https://git.farh.net/groombook/org) skills repository. Read
+those first; this file is only a pointer.
+
+## Authoritative skills
+
+- **SDLC (branching, PRs, phases, handoffs):**
+  [`groombook/org/skills/sdlc/SKILL.md`](https://git.farh.net/groombook/org/src/branch/main/skills/sdlc/SKILL.md)
+- **Coding standards (priority ordering, PR discipline, tests, no-hardcoded-values, CalVer):**
+  [`groombook/org/skills/coding-standards/SKILL.md`](https://git.farh.net/groombook/org/src/branch/main/skills/coding-standards/SKILL.md)
+- **Safety (no plaintext secrets, no direct `kubectl apply` to `groombook`, no self-merge, board approval for destructive actions):**
+  [`groombook/org/skills/safety/SKILL.md`](https://git.farh.net/groombook/org/src/branch/main/skills/safety/SKILL.md)
+
+For human contributors and humans reviewing agent work, see
+[`CONTRIBUTING.md`](./CONTRIBUTING.md) in this repo for the phase-by-phase PR
+flow and the `uat→main` merge-gate policy summary.
+
+## Non-negotiable operational rules
+
+These mirror the org skills; they are restated here so any agent landing in
+this repo sees them without a cross-repo fetch.
+
+- **All changes go through a PR.** Never push directly to `dev`, `uat`, or `main`.
+- **Branch strategy:** `feature/<name>` → `dev` → `uat` → `main`. Engineers
+  always target `dev` first.
+- **No self-merge contract.** The engineer who opened a PR clicks merge only
+  after the named reviewer (CI / QA / UAT / Security / CTO per phase)
+  approves. Issue-thread QA / UAT / security approvals do **not** clear the
+  Gitea `required_approvals` gate on `uat→main` — only a Gitea **Approve**
+  click from a member of the `approvals_whitelist_username` does. On this
+  repo that whitelist is `["gb_flea", "gb_dogfather"]` (engineer team).
+  Board-level accounts cannot give the Approve click by policy.
+- **Always include `cc @cpfarhood`** at the bottom of every PR body for
+  board visibility (not as a reviewer).
+- **Secrets in code are forbidden.** Use Bitnami Sealed Secrets; never commit
+  plaintext. See the `safety` skill.
+- **Production (`groombook` namespace) is Flux-managed.** Never
+  `kubectl apply` directly. Infrastructure changes go through PRs in
+  `groombook/infra`.
+
+## Local development
+
+See the repo's own README, package scripts, and CI workflow. The
+authoritative pipeline (Gitea Actions, image build, deploy hooks) is the
+shared `groombook/infra` overlay; do not reimplement it here.
+
+## When uncertain
+
+If a task conflicts with the org skills, **the org skills win**. Open an
+issue in `groombook/org` to propose a change rather than encoding a local
+exception.