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/examples.go

@@ -0,0 +1,37 @@
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+var examplesCmd = &cobra.Command{
+	Use:   "examples",
+	Short: "Show common usage examples",
+	Args:  cobra.NoArgs,
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Print(`Quick notes:
+  kb "Remember to update DNS records"
+  kb "Server room is building 3" --tags ops
+
+Add files:
+  kb addfile report.pdf
+  kb addfile ~/docs/ --recursive --tags reference
+
+Search:
+  kb search "how to restart nginx"
+  kb search "deploy" --tags ops --top 5
+
+Manage documents:
+  kb list --type pdf
+  kb info 3
+  kb tag 3 --add important,ops
+  kb remove 3 --yes
+`)
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(examplesCmd)
+}