Smoother session onboarding experience (#470)

This PR is a mix of general improvements and temporary frontend trickery
to smooth out the onboarding experience of newly-created sessions until
they reach a `Running` state.

Some of this may become unnecessary once we implement worker pools of
running sessions/pods or something better in the backend. Until then,
this should help a bit.

## Existing experience


https://github.com/user-attachments/assets/b8e2ba28-cc0b-4e28-bd79-5447b123169d

Our current session onboarding experience is a series of toast
notifications, loading states, spinners, elements that pop in, and a
message that very subtly asks the user to select a Workflow to get
started.

If the user finds the Workflow switcher they're rewarded with a "Reload
required" prompt, a "Load new workflow" button to click, and even more
spinners and toasts in the face as they wait for everything to settle
down.

This onboarding currently takes 60+ seconds.

## Improved experience

(Note: the recording below was created early in this PR's life to show
the general flow improvement, some details may change)


https://github.com/user-attachments/assets/bf33046e-8145-44ba-b70b-25de04817395

This PR smooths out the session onboarding experience by getting us a
little closer to @Daniel-Warner-X's original design with in-chat
Workflow suggestions and a static welcome message that appears
immediately.

This gives users something that feels a bit more responsive until we
implement backend improvements that make things actually responsive.
Users may still have to wait a bit for their session's pod to fully spin
up, but this at least gives them more to do and look at while they wait.

Some of the adjustments include:
- A static, instantly-loading welcome message that looks like a regular
chat message but isn't
- A few suggested workflows that a user can read and select without
using the "Workflows" panel
- Removing most loading spinners and states in favor of queuing changes
until the session's pod is `Running`
- Showing the chatbox immediately so users can start typing something
while they wait

---------

Signed-off-by: Michael Clifford <mcliffor@redhat.com>
Co-authored-by: Michael Clifford <mcliffor@redhat.com>

Author: andybraren

components/frontend/package-lock.json

@@ -194,6 +194,27 @@
   }
 }
 
+/* Animation keyframes for welcome experience */
+@keyframes fade-in-up {
+  from {
+    opacity: 0;
+    transform: translateY(20px);
+  }
+  to {
+    opacity: 1;
+    transform: translateY(0);
+  }
+}
+
+@keyframes fade-in-char {
+  from {
+    opacity: 0;
+  }
+  to {
+    opacity: 1;
+  }
+}
+
 /* Thin scrollbar styling - Cross-browser support */
 .scrollbar-thin {
   /* Firefox */