feat(kiosk): plugin.yaml manifest and summer plugin:manifest

- new module kiosk: Manifest, Marshal, Parse, Derive, Generate, Write, Check, StaleError
- plugin:manifest [dir] with --check, --pretend, --name, --description
- docs: kiosk README, root table row, plugins/marketplace.md, scaffolding row

cmd/summer/main.go

@@ -3,9 +3,11 @@ package main
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"os/signal"
+	"path/filepath"
 	"strings"
 	"syscall"
 
@@ -13,6 +15,7 @@ import (
 	"git.golem15.com/golem15/summercms/internal/dev"
 	"git.golem15.com/golem15/summercms/modules/bonfire"
 	"git.golem15.com/golem15/summercms/modules/diary"
+	"git.golem15.com/golem15/summercms/modules/kiosk"
 	"git.golem15.com/golem15/summercms/modules/lagoon"
 )
 
@@ -38,6 +41,7 @@ func toolCommands() []bonfire.Command {
 		makeJobCommand(),
 		makeAdminControllerCommand(),
 		addPluginCommand(),
+		pluginManifestCommand(),
 		newCommand(),
 		devCommand(),
 		parityProxyCommand(),
@@ -414,6 +418,92 @@ already registered is an error.`,
 	}
 }
 
+func pluginManifestCommand() bonfire.Command {
+	return bonfire.Command{
+		Name:        "plugin:manifest",
+		Description: "Generate or check a plugin's plugin.yaml from its sources",
+		Long: `Writes plugin.yaml into a plugin directory (the current one by default). Every
+field comes from the plugin's own sources: the ID and the required plugins
+from what plugin.go's ID() and Requires() return (string literals or
+constants, read without running any code), the module path and the framework
+and plugin version minimums from go.mod, the package import path from the
+directory, and the name and description from the README's H1 and the
+paragraph after it. plugin.yaml is committed next to plugin.go and never
+edited by hand: rerun the command after changing any of those sources.
+
+--name and --description replace the README text and are kept in plugin.yaml
+until changed again; --name="" clears the override. A README whose H1 is the
+plugin ID needs --name. --pretend prints the file without writing it.
+--check writes nothing and exits 1, printing the expected content, when
+plugin.yaml is missing or differs from what the command would write.`,
+		Examples: []bonfire.Example{
+			{Command: "plugin:manifest plugins/acme/blog", Description: "Write plugins/acme/blog/plugin.yaml"},
+			{Command: "plugin:manifest --check", Description: "Fail when the current directory's plugin.yaml is missing or stale"},
+			{Command: "plugin:manifest --pretend", Description: "Print the manifest without writing it"},
+			{Command: `plugin:manifest --name="Blog"`, Description: "Use Blog as the display name instead of the README's H1"},
+		},
+		Args: []bonfire.Arg{{
+			Name:        "dir",
+			Description: "Plugin directory, the one with plugin.go (default: the current directory)",
+		}},
+		Flags: []bonfire.Flag{
+			{Name: "check", Description: "Write nothing; exit 1 when plugin.yaml is missing or stale", Bare: true},
+			{Name: "pretend", Description: "Print the generated plugin.yaml instead of writing it", Bare: true},
+			{Name: "name", Description: "Display name override, kept in plugin.yaml; an empty value clears it"},
+			{Name: "description", Description: "Description override, kept in plugin.yaml; an empty value clears it"},
+		},
+		Run: func(ctx context.Context, in bonfire.Input, out bonfire.Output) error {
+			dir, ok := in.Argument("dir")
+			if !ok || dir == "" {
+				dir = "."
+			}
+			var opts kiosk.DeriveOptions
+			if v, ok := in.Flag("name"); ok {
+				opts.Name = &v
+			}
+			if v, ok := in.Flag("description"); ok {
+				opts.Description = &v
+			}
+			if bonfire.FlagBool(in, "check") {
+				if opts.Name != nil || opts.Description != nil {
+					return fmt.Errorf("plugin:manifest --check takes no --name or --description; run plugin:manifest without --check to change them")
+				}
+				err := kiosk.Check(ctx, dir)
+				var stale *kiosk.StaleError
+				if errors.As(err, &stale) {
+					out.Println("Expected " + stale.Path + ":")
+					out.Println(strings.TrimRight(string(stale.Want), "\n"))
+				}
+				if err != nil {
+					return err
+				}
+				out.Success(filepath.Join(dir, kiosk.FileName) + " is up to date")
+				return nil
+			}
+			if bonfire.FlagBool(in, "pretend") {
+				data, warnings, err := kiosk.Generate(ctx, dir, opts)
+				for _, w := range warnings {
+					out.Warning(w)
+				}
+				if err != nil {
+					return err
+				}
+				out.Println(strings.TrimRight(string(data), "\n"))
+				return nil
+			}
+			path, warnings, err := kiosk.Write(ctx, dir, opts)
+			for _, w := range warnings {
+				out.Warning(w)
+			}
+			if err != nil {
+				return err
+			}
+			out.Success("Wrote " + path)
+			return nil
+		},
+	}
+}
+
 func newCommand() bonfire.Command {
 	return bonfire.Command{
 		Name:        "new",