Initial vault-plugin-secrets-gitea engine

Add a Vault/OpenBao secrets engine that mints ephemeral, scoped Gitea
access tokens on demand. The engine holds a single seeded Gitea site-admin
Basic-Auth credential and, per role, mints a fresh per-user token via the
admin API, bound to a Vault lease and deleted from Gitea on revocation.
Gitea requires Basic Auth for token management (token auth is rejected),
and reqSelfOrAdmin lets a site admin manage any user's tokens, which is the
mechanism this relies on. Gitea tokens never expire server-side, so the
Vault lease is the sole expiry mechanism.

- add backend wiring, config (+ rotate-root), roles, creds paths
- add the gitea client (Basic Auth create/delete token, admin password change)
- add scope validation against Gitea's access-token scope set
- add unit tests (fake Gitea API) and a Vault+OpenBao e2e harness
- add Makefile, nfpm RPM packaging, and Woodpecker build/test/release pipelines

Claude-Session: https://claude.ai/code/session_015ur3i7D2azsMAWTSVABApv

packaging/nfpm.yaml

@@ -0,0 +1,35 @@
+---
+# nfpm config for the vault-plugin-secrets-gitea RPM. Rendered through envsubst
+# (see scripts/build-rpm.sh) then fed to `nfpm pkg`. Built once per target server
+# (Vault, OpenBao); PACKAGE_NAME and PACKAGE_PLUGIN_DIR vary.
+
+name: ${PACKAGE_NAME}
+version: ${PACKAGE_VERSION}
+release: ${PACKAGE_RELEASE}
+arch: ${PACKAGE_ARCH}
+platform: ${PACKAGE_PLATFORM}
+section: default
+priority: extra
+description: "${PACKAGE_DESCRIPTION}"
+
+maintainer: ${PACKAGE_MAINTAINER}
+homepage: ${PACKAGE_HOMEPAGE}
+license: ${PACKAGE_LICENSE}
+
+disable_globbing: false
+
+replaces:
+  - ${PACKAGE_NAME}
+provides:
+  - ${PACKAGE_NAME}
+
+contents:
+  - src: dist/vault-plugin-secrets-gitea
+    dst: ${PACKAGE_PLUGIN_DIR}/vault-plugin-secrets-gitea
+    file_info:
+      mode: 0755
+      owner: root
+      group: root
+
+scripts:
+  preinstall: ${PACKAGE_PREINSTALL}

packaging/scripts/preinstall.sh.tmpl

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Ensure the plugin directory exists before the binary is laid down.
+# Rendered per flavour via envsubst (see scripts/build-rpm.sh).
+mkdir -p ${PACKAGE_PLUGIN_DIR}