feat(web): add Mantine clear buttons to text inputs app-wide (#1333) (#1448)

* feat(web): add Mantine clear buttons to text inputs app-wide (#1333)

Add a clear (×) affordance to every user-editable text input across the
web client so a populated field can be reset in one click.

- Autocomplete: enable `clearable` by default via the theme
  (`theme/Autocomplete.ts`) — covers the prompt-argument and
  resource-template variable autocomplete branches.
- TextInput / Textarea: Mantine v8 does not expose a public `clearable`
  prop on these primitives (only the combobox-based components do), so
  add the clear button manually via `rightSection` + `CloseButton`
  (aria-label="Clear") shown only when the field has a value, wired to
  reset the field's controlled value to "".

Applied to sidebar search inputs (prompts, tools, apps, tasks, history,
resources, network, logs), prompt-argument and resource-template
variable inputs, the sampling response/model fields, server config &
settings forms, roots table, schema form, experimental features panel,
and the server.json import panel. Read-only/display Textareas
(OutputValidationModal, UrlElicitationErrorModal) are intentionally left
untouched.

Tests cover the clear behavior on representative inputs from each
category (sidebar search, prompt argument, resource-template variable,
sampling response, plus the config/settings forms).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(web): disable ServerConfigModal clear buttons while submitting

Address review #2 on #1448: the clear CloseButton sat in `rightSection`
with `rightSectionPointerEvents="auto"`, so it stayed clickable even
while the field was `disabled={submitting}`, letting a user wipe a field
mid-submit. Forward `disabled={submitting}` to each clear button so it
locks together with its input.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(web): remove redundant Auto-respond from SamplingRequestPanel

The sampling modal pre-loads its draft with the default stub result, and
"Send Response" sends that draft — so on an untouched form "Auto-respond"
did exactly the same thing as "Send Response", just with a fresh copy of
the same defaults. Drop the redundant button and its `onAutoRespond` prop;
"Send Response" now covers both the unedited (stub) and edited cases.

The InlineSamplingRequest variant keeps its Auto-respond button — there it
is the quick path versus "Edit & Send" (which opens this editable modal),
not a duplicate of an adjacent send action.

Updated PendingClientRequestModal wiring, stories, and tests accordingly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/web/src/components/groups/SamplingRequestPanel/SamplingRequestPanel.stories.tsx

@@ -18,7 +18,6 @@ const meta: Meta<typeof SamplingRequestPanel> = {
   args: {
     draftResult: defaultDraftResult,
     onResultChange: fn(),
-    onAutoRespond: fn(),
     onSend: fn(),
     onReject: fn(),
   },