server, ui: only offer a working directory when a tool reads it (#26762)

The working directory chip showed up as soon as the server exposed any
builtin tool, so a server started with just get_datetime, or a user who
turned every filesystem tool off in the settings, still got a control
that nothing would read.

Tools now declare whether they resolve their paths and run against the
working directory, next to the write permission they already publish in
the /tools listing. The WebUI shows the chip and enables the /cwd
command only when at least one such tool is both served and left
enabled.

tools/ui/src/lib/hooks/use-chat-form-pickers.svelte.ts

@@ -24,7 +24,7 @@ export interface UseChatFormPickersOptions {
 	/** Gates `/prompt`. */
 	hasPrompts: () => boolean;
 	/** Gates `/cwd`. */
-	hasBuiltinTools: () => boolean;
+	hasCwdTools: () => boolean;
 	getCwd: () => string | null;
 	/** Mention search fallback scope. */
 	getServerHome: () => string | null;
@@ -63,7 +63,7 @@ export function useChatFormPickers(opts: UseChatFormPickersOptions) {
 		getChatCommands({
 			showModelSelector: opts.getShowModelSelector(),
 			hasPrompts: opts.hasPrompts,
-			hasBuiltinTools: opts.hasBuiltinTools
+			hasCwdTools: opts.hasCwdTools
 		})
 	);