Reindex command, implicit note shorthand, add→addfile rename

- Add `kb reindex` command with confirmation prompt and --yes flag
- Add implicit note shorthand: `kb "my note"` submits a note directly
- Rename `add` to `addfile`, remove --note/--title/--type flags
- Add client-side file extension validation before upload
- Add `kb examples` command for common usage patterns
- Update README, SKILL.md, and main specs
- Archive completed changes and sync delta specs

BREAKING: `kb add` renamed to `kb addfile`, `kb add --note` replaced by `kb "text"`

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client/cmd/root.go

@@ -3,6 +3,7 @@ package cmd
 import (
 	"fmt"
 	"os"
+	"strings"
 
 	"github.com/kb-search/kb/internal/api"
 	"github.com/kb-search/kb/internal/config"
@@ -22,9 +23,10 @@ var (
 )
 
 var rootCmd = &cobra.Command{
-	Use:   "kb",
+	Use:   "kb [\"note text\" | command]",
 	Short: "kb-search CLI client",
-	Long:  "A CLI client for the kb-search v2 engine API.",
+	Long:  "A CLI client for the kb-search v2 engine API.\nRun 'kb examples' for common usage patterns.",
+	Args: cobra.ArbitraryArgs,
 	PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
 		if err := config.Load(); err != nil {
 			return err
@@ -32,14 +34,41 @@ var rootCmd = &cobra.Command{
 		config.ApplyFlags(flagEngine, flagFormat, flagAPIKey)
 		return nil
 	},
+	RunE: func(cmd *cobra.Command, args []string) error {
+		if len(args) == 0 {
+			return cmd.Help()
+		}
+		note := strings.Join(args, " ")
+		tags, _ := cmd.Flags().GetString("tags")
+		client := api.NewClient()
+		return submitNote(client, note, tags)
+	},
 }
 
 func init() {
 	api.SetVersionInfo(Version, MinEngineVersion)
 	rootCmd.Version = Version
+	rootCmd.SetUsageTemplate(`Quick note taking:
+  kb "note text" [flags]
+
+Normal usage:
+  kb [command] [flags]{{if .HasAvailableSubCommands}}
+
+Available Commands:{{range .Commands}}{{if (or .IsAvailableCommand (eq .Name "help"))}}
+  {{rpad .Name .NamePadding }} {{.Short}}{{end}}{{end}}{{end}}{{if .HasAvailableLocalFlags}}
+
+Flags:
+{{.LocalFlags.FlagUsages | trimTrailingWhitespaces}}{{end}}{{if .HasAvailableInheritedFlags}}
+
+Global Flags:
+{{.InheritedFlags.FlagUsages | trimTrailingWhitespaces}}{{end}}
+
+Use "{{.CommandPath}} [command] --help" for more information about a command.
+`)
 	rootCmd.PersistentFlags().StringVar(&flagEngine, "engine", "", "engine API URL")
 	rootCmd.PersistentFlags().StringVar(&flagFormat, "format", "", "output format (human|json)")
 	rootCmd.PersistentFlags().StringVar(&flagAPIKey, "api-key", "", "API key for authentication")
+	rootCmd.Flags().String("tags", "", "tags for note shorthand (comma-separated)")
 }
 
 // Execute runs the root command.