Detect always-on reasoning models and show Think button as locked-on (#4654)

* Detect always-on reasoning models and show Think button as locked-on

Models with hardcoded <think>/<think> tags or reasoning_content in
their chat template (e.g. distilled reasoning models) always produce
thinking output regardless of any toggle. Previously these models
were not detected as reasoning-capable at all, so the Think button
was grayed out even though the model was actively reasoning.

Backend:
- Detect <think>/<think> and reasoning_content in GGUF chat templates
  as a fallback when enable_thinking is not present
- Add reasoning_always_on flag to LoadResponse and InferenceStatusResponse
- Pass the flag through all GGUF load and status response paths

Frontend:
- Add reasoningAlwaysOn to the chat runtime store and API types
- When reasoning_always_on is true, show the Think button as lit
  (active) but not clickable, with a tooltip explaining the model
  always uses thinking
- Force reasoningEnabled=true when the model always reasons

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Use pointer-events-none instead of disabled for always-on Think button

The HTML disabled attribute was not fully blocking clicks on the Think
button for always-on reasoning models. Switch to pointer-events-none
CSS class which prevents all mouse interaction at the CSS level.

* Use a static span instead of disabled button for always-on Think

Replace the button element with a plain span when reasoning is
always on. This makes it physically impossible to toggle since
there is no clickable element at all, avoiding any CSS or
disabled-attribute edge cases.

* Simplify always-on Think button to stay lit and remain toggleable

Keep the Think button as a normal toggleable button but ensure it
shows as lit when reasoning_always_on is true. The model always
reasons regardless of the toggle state so there is no need to
block interaction.

---------

Co-authored-by: Daniel Han <danielhanchen@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

studio/frontend/src/features/chat/api/chat-adapter.ts

@@ -307,6 +307,7 @@ async function autoLoadSmallestModel(): Promise<boolean> {
             useChatRuntimeStore.setState({
               ggufContextLength: loadResp.context_length ?? 131072,
               supportsReasoning: loadResp.supports_reasoning ?? false,
+              reasoningAlwaysOn: loadResp.reasoning_always_on ?? false,
               reasoningEnabled: loadResp.supports_reasoning ?? false,
               supportsTools: loadResp.supports_tools ?? false,
               toolsEnabled: loadResp.supports_tools ?? false,
@@ -392,6 +393,7 @@ async function autoLoadSmallestModel(): Promise<boolean> {
       useChatRuntimeStore.setState({
         ggufContextLength: loadResp.context_length ?? 131072,
         supportsReasoning: loadResp.supports_reasoning ?? false,
+        reasoningAlwaysOn: loadResp.reasoning_always_on ?? false,
         reasoningEnabled: loadResp.supports_reasoning ?? false,
         supportsTools: loadResp.supports_tools ?? false,
         toolsEnabled: loadResp.supports_tools ?? false,