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/graph.go

@@ -0,0 +1,71 @@
+package docs
+
+import (
+	"slices"
+	"strings"
+)
+
+// graph checks cross-record rules: unique IDs and supersession.
+func (c *checker) graph(recs []*record) {
+	byStem := map[string][]*record{}
+	byPath := map[string]*record{}
+	for _, r := range recs {
+		byStem[r.stem] = append(byStem[r.stem], r)
+		byPath["/"+r.path] = r
+	}
+	for _, group := range byStem {
+		for _, r := range group {
+			for _, o := range group {
+				if o != r {
+					c.add(r.path, 1, "duplicate ID %s, also used by %s", r.stem, o.path)
+				}
+			}
+		}
+	}
+	adrs := recs[:0:0]
+	for _, r := range recs {
+		if r.kind == "adr" && r.fm != nil {
+			adrs = append(adrs, r)
+		}
+	}
+	for _, r := range adrs {
+		if len(r.lists["supersedes"]) > 0 && !slices.Contains([]string{"accepted", "superseded", "deprecated"}, r.status) {
+			c.add(r.path, r.fm.line("supersedes"), "a record that supersedes another must be accepted, superseded or deprecated, not %s", r.status)
+		}
+		for _, e := range [][2]string{{"supersedes", "superseded_by"}, {"superseded_by", "supersedes"}} {
+			for _, it := range r.lists[e[0]] {
+				if o := byPath[it.v]; o != nil && o.kind == "adr" && !slices.ContainsFunc(o.lists[e[1]], func(x item) bool { return x.v == "/"+r.path }) {
+					c.add(r.path, it.line, "%s lists %s, which must list this record in %s", e[0], it.v, e[1])
+				}
+			}
+		}
+	}
+	// Cycles over supersedes edges: report once, on the first record (in path order) that closes one.
+	const (
+		visiting = 1
+		done     = 2
+	)
+	state := map[*record]int{}
+	var visit func(r *record)
+	visit = func(r *record) {
+		state[r] = visiting
+		for _, it := range r.lists["supersedes"] {
+			o := byPath[it.v]
+			if o == nil || o.kind != "adr" {
+				continue
+			}
+			switch state[o] {
+			case visiting:
+				c.add(r.path, it.line, "supersession cycle through %s", strings.TrimPrefix(it.v, "/"))
+			case 0:
+				visit(o)
+			}
+		}
+		state[r] = done
+	}
+	for _, r := range adrs {
+		if state[r] == 0 {
+			visit(r)
+		}
+	}
+}