feat: add docs checker and record templates

docs new creates ADRs and plans from embedded templates; docs check reports
path:line: message problems per docs/docs-format.md.

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

internal/docs/adr.go

@@ -0,0 +1,45 @@
+package docs
+
+import "time"
+
+var (
+	adrStatuses = []string{"proposed", "accepted", "rejected", "deprecated", "superseded"}
+	adrImpls    = []string{"not-started", "in-progress", "implemented", "deferred", "not-applicable"}
+	adrRefs     = []refSpec{
+		{"supersedes", kAdr}, {"superseded_by", kAdr}, {"related", kAdr | kPlan},
+		{"tracking", kPlan | kURL}, {"implemented_by", kURL | kFile},
+	}
+)
+
+// adr checks the ADR frontmatter and returns its title for the body check.
+func (c *checker) adr(r *record, m *fm) (string, bool) {
+	m.keys("title", "date", "status", "implementation", "summary", "tags", "supersedes", "superseded_by", "related", "tracking", "implemented_by")
+	title, titleOK := m.text("title")
+	if d, line, ok := m.scalar("date"); ok {
+		if _, err := time.Parse(time.DateOnly, d); err != nil || len(d) != len(time.DateOnly) {
+			c.add(r.path, line, "date must be a valid YYYY-MM-DD date")
+		} else if d != r.date {
+			c.add(r.path, line, "date %s does not match the filename date %s", d, r.date)
+		}
+	}
+	status, statusOK := m.enum("status", adrStatuses...)
+	impl, implOK := m.enum("implementation", adrImpls...)
+	m.text("summary")
+	m.tags()
+	m.refs(adrRefs...)
+	r.status = status
+	if statusOK {
+		if n := len(r.lists["superseded_by"]); status == "superseded" && n == 0 {
+			m.problemf("status", "status superseded requires superseded_by")
+		} else if status != "superseded" && n > 0 {
+			m.problemf("superseded_by", "superseded_by requires status superseded")
+		}
+		if status == "rejected" && implOK && impl != "not-applicable" {
+			m.problemf("implementation", "status rejected requires implementation not-applicable")
+		}
+	}
+	if implOK && impl == "implemented" && len(r.lists["implemented_by"]) == 0 {
+		m.problemf("implementation", "implementation implemented requires implemented_by")
+	}
+	return title, titleOK
+}