Replace implicit note shorthand with explicit addnote command and split README

Two changes:

1. structured-add-commands: The implicit note shorthand (kb "text") caused
   accidental note creation from mistyped commands. Replaced with explicit
   kb addnote <text> command. Root command reverts to standard Cobra
   behaviour. Updated examples, tests, SKILL.md, and specs.

2. split-readme-developer-docs: Moved build-from-source instructions, release
   process, API reference, and ROCm migration notes from README.md into a
   new DEVELOPER.md. README now links to DEVELOPER.md for dev workflows.

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

client/cmd/root_test.go

@@ -6,36 +6,6 @@ import (
 	"testing"
 )
 
-func TestRootCmd_SingleWordRejected(t *testing.T) {
-	rootCmd.SetArgs([]string{"infow"})
-
-	var stderr bytes.Buffer
-	rootCmd.SetErr(&stderr)
-
-	err := rootCmd.Execute()
-	if err == nil {
-		t.Fatal("expected error for single bare word, got nil")
-	}
-
-	errMsg := err.Error()
-	if !strings.Contains(errMsg, `unknown command "infow"`) {
-		t.Errorf("expected error to mention unknown command, got: %s", errMsg)
-	}
-	if !strings.Contains(errMsg, "multiple words") {
-		t.Errorf("expected error to suggest multiple words, got: %s", errMsg)
-	}
-}
-
-func TestRootCmd_MultipleWordsNotRejected(t *testing.T) {
-	rootCmd.SetArgs([]string{"remember", "to", "update", "dns"})
-
-	err := rootCmd.Execute()
-	// Will fail at API call (no server), but should NOT be the "unknown command" error
-	if err != nil && strings.Contains(err.Error(), "unknown command") {
-		t.Errorf("multi-word input should not be rejected as unknown command, got: %s", err.Error())
-	}
-}
-
 func TestRootCmd_NoArgs_ShowsHelp(t *testing.T) {
 	rootCmd.SetArgs([]string{})
 
@@ -52,3 +22,48 @@ func TestRootCmd_NoArgs_ShowsHelp(t *testing.T) {
 		t.Errorf("expected help output, got: %s", output)
 	}
 }
+
+func TestRootCmd_UnknownCommand_ReturnsError(t *testing.T) {
+	rootCmd.SetArgs([]string{"notacommand"})
+
+	var stderr bytes.Buffer
+	rootCmd.SetErr(&stderr)
+
+	err := rootCmd.Execute()
+	if err == nil {
+		t.Fatal("expected error for unknown command, got nil")
+	}
+
+	errMsg := err.Error()
+	if !strings.Contains(errMsg, "unknown command") {
+		t.Errorf("expected 'unknown command' error, got: %s", errMsg)
+	}
+}
+
+func TestAddnoteCmd_NoArgs_ReturnsError(t *testing.T) {
+	rootCmd.SetArgs([]string{"addnote"})
+
+	err := rootCmd.Execute()
+	if err == nil {
+		t.Fatal("expected error for addnote with no args, got nil")
+	}
+
+	errMsg := err.Error()
+	if !strings.Contains(errMsg, "requires a note text argument") {
+		t.Errorf("expected 'requires a note text argument' error, got: %s", errMsg)
+	}
+}
+
+func TestAddnoteCmd_TooManyArgs_ReturnsError(t *testing.T) {
+	rootCmd.SetArgs([]string{"addnote", "hello", "world"})
+
+	err := rootCmd.Execute()
+	if err == nil {
+		t.Fatal("expected error for addnote with too many args, got nil")
+	}
+
+	errMsg := err.Error()
+	if !strings.Contains(errMsg, "quote your note text") {
+		t.Errorf("expected 'accepts 1 arg' error, got: %s", errMsg)
+	}
+}