suite init и suite add: заведение набора и конвенции в двух режимах

- suite init создаёт директорию и манифест со скелетом таблиц; suite add пишет
  файл конвенции и вправляет запись в suite.toml, сохраняя комментарии
- без аргументов команды спрашивают поля с подсказками, с флагами берут всё
  сразу и не спрашивают ничего; без терминала пустой вызов отказывает
- строка о версии языка генерируется из словаря набора, поэтому созданный файл
  проходит suite check без правок
- починено разрешение extends: короткая форма бралась по суффиксу и могла
  указать на сам файл; теперь неоднозначность либо избегается при записи, либо
  сообщается ошибкой

internal/manifest/edit.go

@@ -0,0 +1,115 @@
+package manifest
+
+import (
+	"fmt"
+	"regexp"
+	"slices"
+	"sort"
+	"strings"
+)
+
+// The manifest is edited as text rather than decoded and written back.
+//
+// suite.toml carries more comment than data — the reasoning behind every topic
+// and every prefix lives there, and an encoder would drop all of it and reorder
+// what is left. So an entry is spliced into the source, and everything the
+// author wrote around it survives untouched.
+
+var (
+	tableRe = regexp.MustCompile(`^\s*\[([^\]]+)\]\s*$`)
+	keyRe   = regexp.MustCompile(`^\s*("[^"]+"|[A-Za-z0-9_-]+)\s*=`)
+	bareRe  = regexp.MustCompile(`^[A-Za-z0-9_-]+$`)
+)
+
+// AddEntry splices key = "value" into the given table of a TOML source.
+//
+// Where the entry lands follows what the table already does: a table whose keys
+// are in alphabetical order keeps it, and one ordered by hand — by directory,
+// by age, by whatever the author meant — gets the entry appended, because
+// guessing at that order would scatter it.
+func AddEntry(source []byte, table, key, value string) ([]byte, error) {
+	lines := strings.Split(string(source), "\n")
+
+	start := -1
+	for i, line := range lines {
+		if m := tableRe.FindStringSubmatch(line); m != nil && m[1] == table {
+			start = i
+			break
+		}
+	}
+	if start < 0 {
+		return nil, fmt.Errorf("the manifest holds no table [%s]", table)
+	}
+
+	end := len(lines)
+	for i := start + 1; i < len(lines); i++ {
+		if tableRe.MatchString(lines[i]) {
+			end = i
+			break
+		}
+	}
+
+	keys, at := tableKeys(lines, start+1, end)
+	if slices.Contains(keys, key) {
+		return nil, fmt.Errorf("the table [%s] already holds the key %s", table, key)
+	}
+
+	entry := renderEntry(key, value)
+	insert := insertionPoint(keys, at, key, lines, start, end)
+
+	out := make([]string, 0, len(lines)+1)
+	out = append(out, lines[:insert]...)
+	out = append(out, entry)
+	out = append(out, lines[insert:]...)
+	return []byte(strings.Join(out, "\n")), nil
+}
+
+// tableKeys collects the keys of a table together with the line each sits on.
+func tableKeys(lines []string, from, to int) (keys []string, at []int) {
+	for i := from; i < to; i++ {
+		m := keyRe.FindStringSubmatch(lines[i])
+		if m == nil {
+			continue
+		}
+		keys = append(keys, strings.Trim(m[1], `"`))
+		at = append(at, i)
+	}
+	return keys, at
+}
+
+// insertionPoint picks the line the entry goes before.
+func insertionPoint(keys []string, at []int, key string, lines []string, start, end int) int {
+	if len(keys) == 0 {
+		// An empty table owns the comments standing right under its header
+		// and nothing further: a comment block separated by a blank line
+		// belongs to the table header below it, not to this one. Walking to
+		// the end of the section instead would file the entry under the wrong
+		// explanation.
+		i := start + 1
+		for i < end && strings.HasPrefix(strings.TrimSpace(lines[i]), "#") {
+			i++
+		}
+		return i
+	}
+	if sort.StringsAreSorted(keys) {
+		for i, existing := range keys {
+			if key < existing {
+				return at[i]
+			}
+		}
+	}
+	return at[len(at)-1] + 1
+}
+
+// renderEntry writes one key-value line, quoting the key when it is not bare.
+func renderEntry(key, value string) string {
+	if !bareRe.MatchString(key) {
+		key = `"` + escape(key) + `"`
+	}
+	return key + ` = "` + escape(value) + `"`
+}
+
+func escape(s string) string {
+	s = strings.ReplaceAll(s, `\`, `\\`)
+	return strings.ReplaceAll(s, `"`, `\"`)
+}