Unify deployment tracking and support multiple deployments (#677)

This change centralizes deployment state management and enables seamless
multi-deployment support. The extension now properly tracks
per-deployment credentials, syncs state across VS Code windows, and
handles login/logout flows in a unified way.

Key changes:

Architecture:
- Add `DeploymentManager` to centralize deployment state (`url`,
`label`, `token`, `user`) and coordinate extension client updates, auth
contexts, and workspace refreshes
- Add `LoginCoordinator` to handle login prompts with cross-window
detection, preventing duplicate login dialogs when multiple windows need
auth

Storage & Auth:
- `SecretsManager` now stores per-deployment credentials using
label-based keys (`coder.session.<label>`) instead of flat
`sessionToken` storage
- Add LRU tracking for deployments with automatic cleanup of old
credentials
- Add migration from legacy flat storage format
- Cross-window sync via `secrets.onDidChange` events
- Debug command (`coder.debug.listDeployments`) for inspecting stored
state

Commands & Remote:
- Commands now use `DeploymentManager` instead of directly manipulating
client
- Remote connection uses `LoginCoordinator` for auth prompts during
workspace connections
- `CliManager.configure()` now called on every remote connection, with
secrets storage as the source of truth for credentials

WebSocket improvements:
- `CoderApi` now implements Disposable to clean up WebSocket connections
- Add `setCredentials()` method to update host+token atomically,
avoiding unnecessary reconnection cycles
- Add `disconnect()` support to `ReconnectingWebSocket` for clean
disconnects
- Simplify WebSocket fallback logic with cleaner SSE fallback handling

Tests:
- Update `secretsManager` tests for new per-deployment API
- Add comprehensive `reconnectingWebSocket` tests for disconnect/reconnect
- Extend `coderApi` tests for credential handling

Author: EhabY

package.json

@@ -265,10 +265,19 @@
 				"title": "Search",
 				"category": "Coder",
 				"icon": "$(search)"
+			},
+			{
+				"command": "coder.debug.listDeployments",
+				"title": "List Stored Deployments",
+				"category": "Coder Debug"
 			}
 		],
 		"menus": {
 			"commandPalette": [
+				{
+					"command": "coder.debug.listDeployments",
+					"when": "coder.devMode"
+				},
 				{
 					"command": "coder.openFromSidebar",
 					"when": "false"