collapsible kino centre panel

[matt-beanland]

the artefact panel should be collapsible, it should default collapsed

[matt-beanland]

Summary
ArtefactKino Inspector panel is now collapsible, matching the existing Export panel. Both side panels default collapsed so the graph gets the full kino width on bigger artefacts. Selecting a node or relationship in the graph auto-expands the Inspector to the matching row.
Design
Layout
The Inspector panel header now hosts a collapse button (▶ when collapsed, ◀ when expanded) sitting at the right of the tab row, mirroring the Export panel's existing collapse pattern. When collapsed, the panel shrinks to a 32px-wide strip showing only the collapse button; clicking it expands the panel back to its flex: 1 share.
Both side panels start collapsed by default — no opt — so first render on a big graph fills the available width with the graph itself.
Behaviour
Clicking a node in the graph or selecting a relationship calls inspectorControl.expand() before renderTab(...), so the panel auto-pops if the user has it collapsed. Manual collapse is preserved between selections; auto-expand only kicks in when the panel is currently collapsed.
Implementation
The two parallel collapse code paths are folded into a single setupCollapse(panel, button, hideSelectors, defaultCollapsed) helper inside the Kino's JS asset. Each panel registers its own control via the helper; the inspector's control is captured in scope so the network event handlers can call inspectorControl.expand().
btnStyle uses el.style.cssText = ... which wipes inline styles, so setupCollapse reapplies marginLeft = "auto" after btnStyle to keep the button pinned to the right of the header strip when it is the only visible child.
The Inspector header gained padding:4px;justify-content:flex-end;gap:4px; to give the lone collapse button breathing room and a clean right-edge position when the tab buttons are hidden.
Dependency
mix.exs artefact_dep/0 bumped from ~> 0.1.3 to > 0.1.4 in both the HEX_PUBLISH=1 branch and the published-default branch. Path-dep branch (File.exists?(.../artefact/mix.exs)) is unchanged for monorepo dev. Not strictly required by 0.1.4 (kino's API surface is unchanged); the bump is for convenience so users pulling {:artefact_kino, "> 0.1.4"} get Artefact.graft/3 transitively.
Files changed
artefact_kino/lib/artefact_kino.ex # inspector collapse, helper refactor, auto-expand wiring
artefact_kino/mix.exs # @Version 0.1.4, artefact dep ~> 0.1.4
artefact_kino/CHANGELOG.md # 0.1.4 entry
artefact_kino/README.md # collapsibility paragraph + Mermaid mention in Export bullet