Add stroked 24x24 SVGs for the activity rail (objects, traces, sections,
3D scene, settings), the tool rail's Flag and Host tiles, the section-nav
chevrons, and the Objects-panel search field. They render through the
existing tinted-icon path, so the Studio rails use vector line icons rather
than the mockup's placeholder glyphs. Flag and Host now resolve to icons;
update the icon tests to match and to assert the Studio icon set is present.

Add the gui/studio package implementing the Studio layout grammar: the
activity rail; the first-class filterable Objects panel (model/view + a
delegate that draws swatch, name, faint mono type, and a curation status dot,
with a teal-bar selection and a curation legend); the dark canvas with glassy
floating controls (active-object badge, scale bar, section-nav pill, and a
brightness/contrast card with teal thumbs); the flush tool rail; the
trace-palette strip; the mono status bar; and a title strip, all assembled by
StudioShell.

The widgets are a pure view layer (PySide6 plus the theme/icon utilities
only), driven by data setters and signals, so they construct headlessly and
can be adopted by the main window. Chrome comes from studio_tokens through a
single QSS template; a theme toggle swaps the Studio (dark) and Atlas (light)
shell around the always-dark canvas.

Add dev/studio_preview.py to render both shells offscreen, and headless tests
covering the structure and the non-negotiables (row anatomy, flush tool rail,
zero azure, theme toggle, and honest 3D/Settings seams).

Add Studio (dark) and Atlas (light) to the theme radio in both the View-menu
theme dialog and the options dialog, persisted through the existing "theme"
setting. This makes the new token layer selectable in the running app while
the bespoke Studio layout widgets are adopted into the main window separately.

Replace the title strip's placeholder conic-gradient mark with the shipped
PyReconstruct app icon — the dark-glass squircle on the Studio shell, the light
squircle on Atlas, mirroring how the main window chooses the OS window icon —
and set it as the shell's window icon so the real window decoration carries it
too. Falls back to the conic mark if the asset can't be loaded. The icon path
is resolved relative to the package, so the view layer gains no new dependency.

…ark gap

Swap the title strip's squircle app icon for the bare transparent fork logo
(logo.png), which reads on both the dark and light title bars, and use it as
the window icon too. Collapse the "Py" / "Reconstruct" wordmark into a single
rich-text label so they render as one word — previously the layout's item
spacing (plus a stray zero-width spacer) opened a visible gap between them.
"Reconstruct" keeps the teal accent, re-tinted with the theme.