fix(coding-agent): remove process-cwd tool singletons and use tool-name allowlists

- switch SDK/CLI tool selection to name-based allowlists
- apply allowlists across built-in, extension, and SDK tools
- remove ambient process.cwd defaults from core tooling and resource helpers
- update tests, examples, and TUI callers for explicit cwd plumbing
- add regression coverage for extension tool filtering

closes #3452
closes #2835

packages/coding-agent/src/core/tools/grep.ts

@@ -382,7 +382,3 @@ export function createGrepToolDefinition(
 export function createGrepTool(cwd: string, options?: GrepToolOptions): AgentTool<typeof grepSchema> {
 	return wrapToolDefinition(createGrepToolDefinition(cwd, options));
 }
-
-/** Default grep tool using process.cwd() for backwards compatibility. */
-export const grepToolDefinition = createGrepToolDefinition(process.cwd());
-export const grepTool = createGrepTool(process.cwd());