refactor: remove agents TUI (#25190)

cli/testdata/coder_--help.golden

@@ -14,7 +14,6 @@ USAGE:
        $ coder templates init
 
 SUBCOMMANDS:
-    agents            Interactive terminal UI for AI agents.
     autoupdate        Toggle auto-update policy for a workspace
     completion        Install or update shell completion scripts for the
                       detected or chosen shell.

cli/testdata/coder_agents_--help.golden

@@ -1,16 +0,0 @@
-coder v0.0.0-devel
-
-USAGE:
-  coder agents [flags] [chat-id]
-
-  Interactive terminal UI for AI agents.
-
-OPTIONS:
-      --model string
-          Choose a model by ID, provider/model, or display name.
-
-      --workspace string
-          Associate the chat with a workspace by name, owner/name, or UUID.
-
-———
-Run `coder --help` for a list of global options.