feat(sidebar): add persistent project-aware sidebar interface

README.org

@@ -216,6 +216,41 @@ Start an agent shell session:
 - =M-x agent-shell-google-start-gemini= - Start a Gemini agent session
 - =M-x agent-shell-goose-start-agent= - Start a Goose agent session
 
+*** Sidebar
+
+=agent-shell-sidebar= provides a persistent side panel interface. Each project gets its own independent sidebar that maintains separate state across visibility toggles.
+
+Commands:
+
+- =M-x agent-shell-sidebar-toggle= - Toggle sidebar visibility for current project
+- =M-x agent-shell-sidebar-toggle-focus= - Toggle focus between sidebar and last buffer
+- =M-x agent-shell-sidebar-change-provider= - Switch to a different agent provider
+- =M-x agent-shell-sidebar-reset= - Reset sidebar for current project
+
+Configuration options:
+
+#+begin_src emacs-lisp
+;; Sidebar width (default: "25%")
+;; Integer for absolute columns or string with % for percentage of frame
+(setq agent-shell-sidebar-width "25%")
+
+;; Minimum width (default: 80)
+(setq agent-shell-sidebar-minimum-width 80)
+
+;; Maximum width (default: "50%")
+(setq agent-shell-sidebar-maximum-width "50%")
+
+;; Position: 'left or 'right (default: 'right)
+(setq agent-shell-sidebar-position 'right)
+
+;; Default provider (default: nil - prompt user)
+;; Values: 'anthropic-claude-code, 'google-gemini, 'openai-codex, 'goose-agent
+(setq agent-shell-sidebar-default-provider 'anthropic-claude-code)
+
+;; Lock sidebar position and size (default: t)
+(setq agent-shell-sidebar-locked t)
+#+end_src
+
 ** Running agents in Devcontainers / Docker containers (Experimental)
 
 =agent-shell= provides rudimentary support for running agents in containers.