refactor: CLI-mediate credentials and move global-config to globalFlags

Replace the dedicated `coder.globalConfig` setting with a `--global-config`
passthrough in `coder.globalFlags`, honored on 2.31.0+. The extension no longer
reads/writes the CLI credential files itself: it writes via `coder login`
(0.25.0+, `--use-token-as-session`), reads via `coder login token` (2.31.0+),
and deletes via `coder logout` (keyring or file with `--global-config`).
Direct file writes remain only as a pre-0.25 fallback. The binary cache no
longer follows the config dir.

Author: EhabY

package.json

@@ -181,14 +181,8 @@
 					],
 					"scope": "machine"
 				},
-				"coder.globalConfig": {
-					"markdownDescription": "Path to the global Coder CLI config directory passed with `--global-config`. Defaults to `CODER_CONFIG_DIR` if not set, otherwise the extension's per-deployment global storage directory. Set this to a shared CLI config directory such as `~/.config/coderv2` to share login/auth with the Coder CLI. Ignored when `#coder.useKeyring#` is active and supported.\n\nSupports `${env:VAR}`, `${userHome}`, and a leading `~`.",
-					"type": "string",
-					"default": "",
-					"scope": "machine"
-				},
 				"coder.globalFlags": {
-					"markdownDescription": "Global flags to pass to every Coder CLI invocation. Enter each flag as a separate array item, in order. Do **not** include the `coder` command itself. See the [CLI reference](https://coder.com/docs/reference/cli) for available global flags.\n\nSupports `${env:VAR}`, `${userHome}`, and a leading `~`. For `--flag=value` items the expansion applies to the value half, so `--cfg=~/coder` works.\n\nFor `--header-command`, precedence is: `#coder.headerCommand#` setting, then `CODER_HEADER_COMMAND` environment variable, then the value specified here. The `--global-config` and `--use-keyring` flags are silently ignored; use `#coder.globalConfig#` and `#coder.useKeyring#` instead.",
+					"markdownDescription": "Global flags to pass to every Coder CLI invocation. Enter each flag as a separate array item, in order. Do **not** include the `coder` command itself. See the [CLI reference](https://coder.com/docs/reference/cli) for available global flags.\n\nSupports `${env:VAR}`, `${userHome}`, and a leading `~`. For `--flag=value` items the expansion applies to the value half, so `--cfg=~/coder` works.\n\nSet `--global-config` here to point the CLI at a shared config directory (e.g. `--global-config=~/.config/coderv2` to share login/auth with the Coder CLI); requires a deployment on 2.31.0+ and is ignored when `#coder.useKeyring#` is active. The `--use-keyring` flag is ignored; use `#coder.useKeyring#` instead.\n\nFor `--header-command`, precedence is: `#coder.headerCommand#` setting, then `CODER_HEADER_COMMAND` environment variable, then the value specified here.",
 					"type": "array",
 					"items": {
 						"type": "string"