rebrand: sweep remaining switchboard refs + rename cookies/storage keys

- CSS headers (4 files): Switchboard Core → Armature
- Editor .mjs headers (8 files): Chat Switchboard → Armature
- SQL migration comments + seed data (20 files): Switchboard Core → Armature
- Webhook header: X-Switchboard-Event → X-Armature-Event
- Cookie: sb_token → arm_token (3 Go files + auth.js)
- localStorage: sb_auth → arm_auth (auth.js + 2 test runners)
- localStorage: switchboard_theme → armature_theme (theme.js + base.html)
- Debug engine filter: chatSwitchboard/switchboard/sb_ → armatureChat/armature/arm_
- JS export: switchboardTheme → armatureTheme (theme.mjs + code-editor.mjs)

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

server/middleware/auth.go

@@ -142,11 +142,11 @@ func parseAndValidateJWT(tokenString string, jwtSecret string) (*Claims, bool) {
 	return claims, true
 }
 
-// UserIDFromCookie extracts the user ID from the sb_token cookie without
+// UserIDFromCookie extracts the user ID from the arm_token cookie without
 // requiring authentication. Returns "" if no valid token is found.
 // Used by unauthenticated routes that want optional user context.
 func UserIDFromCookie(c *gin.Context, jwtSecret string) string {
-	cookie, err := c.Cookie("sb_token")
+	cookie, err := c.Cookie("arm_token")
 	if err != nil || cookie == "" {
 		return ""
 	}