feat: add CLI commands to manage AI Gateway keys (#25689)

Adds `coder ai-gateway keys` commands:
* `create <name>` creates key with given name
* `list` lists existing keys (alias `ls`)
* `delete <name | id>` removes key matching by name or key id, name has
priority (alias `rm`)

enterprise/cli/testdata/coder_--help.golden

@@ -16,6 +16,7 @@ USAGE:
 SUBCOMMANDS:
     agent-firewall         Network isolation tool for monitoring and restricting
                            HTTP/HTTPS requests
+    ai-gateway             Manage AI Gateway
     external-workspaces    Create or manage external workspaces
     features               List Enterprise features
     groups                 Manage groups

enterprise/cli/testdata/coder_ai-gateway_--help.golden

@@ -0,0 +1,12 @@
+coder v0.0.0-devel
+
+USAGE:
+  coder ai-gateway
+
+  Manage AI Gateway
+
+SUBCOMMANDS:
+    keys    Manage AI Gateway keys
+
+———
+Run `coder --help` for a list of global options.

enterprise/cli/testdata/coder_ai-gateway_keys_--help.golden

@@ -0,0 +1,14 @@
+coder v0.0.0-devel
+
+USAGE:
+  coder ai-gateway keys
+
+  Manage AI Gateway keys
+
+SUBCOMMANDS:
+    create    Create an AI Gateway key
+    delete    Delete an AI Gateway key
+    list      List AI Gateway keys
+
+———
+Run `coder --help` for a list of global options.

enterprise/cli/testdata/coder_ai-gateway_keys_create_--help.golden

@@ -0,0 +1,9 @@
+coder v0.0.0-devel
+
+USAGE:
+  coder ai-gateway keys create <name>
+
+  Create an AI Gateway key
+
+———
+Run `coder --help` for a list of global options.

enterprise/cli/testdata/coder_ai-gateway_keys_delete_--help.golden

@@ -0,0 +1,15 @@
+coder v0.0.0-devel
+
+USAGE:
+  coder ai-gateway keys delete [flags] <name|id>
+
+  Delete an AI Gateway key
+
+  Aliases: rm
+
+OPTIONS:
+  -y, --yes bool
+          Bypass confirmation prompts.
+
+———
+Run `coder --help` for a list of global options.

enterprise/cli/testdata/coder_ai-gateway_keys_list_--help.golden

@@ -0,0 +1,18 @@
+coder v0.0.0-devel
+
+USAGE:
+  coder ai-gateway keys list [flags]
+
+  List AI Gateway keys
+
+  Aliases: ls
+
+OPTIONS:
+  -c, --column [id|name|key prefix|created at|last used at] (default: id,name,key prefix,last used at,created at)
+          Columns to display in table output.
+
+  -o, --output table|json (default: table)
+          Output format.
+
+———
+Run `coder --help` for a list of global options.