feat: add docs checker for ADRs and implementation plans (#1)

Add cmd/docs, the first corestack component: `docs new adr|plan "Title"`
writes records from embedded templates, and `docs check` validates them
against the public format spec in docs/docs-format.md (timestamp IDs,
frontmatter keys and enums, separate decision and implementation status,
supersession symmetry, MADR 4 layout with required Consequences, plan
sections, and repo-root/durable references), reporting path:line errors.

Also adds the module skeleton (go.auvem.com/corestack, BSD-3-Clause,
README, AGENTS.md, CLAUDE.md), Gitea CI running tests and docs check,
a tag-triggered goreleaser release for darwin/linux binaries, and the
accepted ADR adopting the format.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -0,0 +1,31 @@
+name: ci
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7.0.1
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-go@v7.0.0
+        with:
+          go-version-file: go.mod
+      - name: gofmt
+        run: test -z "$(gofmt -l .)"
+      - run: go vet ./...
+      - run: go test -race ./...
+      - run: go run ./cmd/docs check
+      - uses: goreleaser/goreleaser-action@v7.3.0
+        with:
+          distribution: goreleaser
+          version: v2.19.0
+          args: check
+      - uses: goreleaser/goreleaser-action@v7.3.0
+        with:
+          distribution: goreleaser
+          version: v2.19.0
+          args: release --snapshot --clean