feat(webapp): AI agent logo experiments (#4399)

## Summary

Adds an admin-only "AI agent" storybook page exploring an animated
identity for the dashboard agent: a resting dot logo that animates while
the agent is thinking, then settles once it is done.

The lead experiment is a 5x5 dot matrix. Shapes are five-line string
bitmaps, a bright head walks each shape's route on a fixed beat, and it
only hands off between shapes on a dot the two share, so the rhythm
never breaks. It comes with 26 faces, six gradient palettes, and light
and dark treatments. Two earlier prototypes (a crisp logo that scatters
into orbiting dots, and a dotted triangle on tilted 3D orbits) are kept
in their own tabs for comparison. Everything is plain canvas code with
no new dependencies.

Also adds an `ask-ai` Button variant: secondary styling with a soft
trigger-green border and padding tuned around the leading logo. The
variant supplies the agent logo itself, so callers write `<Button
variant="ask-ai/small">Ask AI</Button>`. Passing a `LeadingIcon`
overrides it, which is how the thinking animation gets driven.

No release note: the storybook is admin gated and the button variant is
not used in product UI yet.

Author: samejr