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>

internal/docs/plan.go

@@ -0,0 +1,23 @@
+package docs
+
+var planRefs = []refSpec{{"tracking", kURL}, {"adrs", kAdr}, {"completion", kURL | kFile}}
+
+func (c *checker) plan(r *record, m *fm) {
+	m.keys("status", "tracking", "adrs", "completion")
+	status, ok := m.enum("status", "draft", "active", "completed", "cancelled")
+	m.refs(planRefs...)
+	r.status = status
+	if !ok {
+		return
+	}
+	closed := status == "completed" || status == "cancelled"
+	if status == "active" && len(r.lists["tracking"]) == 0 {
+		m.problemf("status", "status active requires tracking")
+	}
+	if closed && len(r.lists["completion"]) == 0 {
+		m.problemf("status", "status %s requires completion", status)
+	}
+	if !closed && len(r.lists["completion"]) > 0 {
+		m.problemf("completion", "completion must be empty while status is %s", status)
+	}
+}