feat(cli): support app_url in CLI config (#186)

* feat(cli): support app_url in CLI config for browser login

The login flow opens the frontend URL for browser-based auth, but
previously app_url could only be set via environment variables.
Add app_url to CLIConfig so it can be persisted with `multica config set`.

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

* fix(cli): persist app_url to config during browser login

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

---------

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

server/internal/cli/config.go

@@ -19,6 +19,7 @@ type WatchedWorkspace struct {
 // CLIConfig holds persistent CLI settings.
 type CLIConfig struct {
 	ServerURL          string             `json:"server_url,omitempty"`
+	AppURL             string             `json:"app_url,omitempty"`
 	WorkspaceID        string             `json:"workspace_id,omitempty"`
 	Token              string             `json:"token,omitempty"`
 	WatchedWorkspaces  []WatchedWorkspace `json:"watched_workspaces,omitempty"`