fix(ui): keep empty canvases visible

ui_server.py

@@ -1318,7 +1318,7 @@ HTML = """<!doctype html>
     .config-deleted-list { display: grid; gap: 5px; padding-top: 4px; border-top: 1px solid var(--ui-border); }
     .config-deleted-list[hidden] { display: none !important; }
     .config-restore-panel[hidden], .config-trash[hidden] { display: none !important; }
-    .config-canvas { position: relative; display: block; min-height: 760px; padding: 8px 6px 18px; overflow: auto; overscroll-behavior: auto; background: radial-gradient(circle at 12% 8%, color-mix(in srgb, var(--ui-accent) 7%, transparent), transparent 28%), linear-gradient(135deg, color-mix(in srgb, var(--ui-bg) 74%, var(--ui-panel)), var(--ui-bg)); }
+    .config-canvas { position: relative; display: block; min-height: max(760px, calc(100dvh - 144px)); padding: 8px 6px 18px; overflow: auto; overscroll-behavior: auto; background: radial-gradient(circle at 12% 8%, color-mix(in srgb, var(--ui-accent) 7%, transparent), transparent 28%), linear-gradient(135deg, color-mix(in srgb, var(--ui-bg) 74%, var(--ui-panel)), var(--ui-bg)); background-color: var(--ui-bg); }
     .config-canvas::before { content: ""; position: absolute; inset: 0; z-index: 0; pointer-events: none; opacity: .34; background-image: linear-gradient(color-mix(in srgb, var(--ui-text) 5%, transparent) 1px, transparent 1px), linear-gradient(90deg, color-mix(in srgb, var(--ui-text) 5%, transparent) 1px, transparent 1px); background-size: 28px 28px; mask-image: linear-gradient(to bottom, black, transparent 86%); }
     .config-canvas > .config-block { position: absolute; z-index: 1; box-sizing: border-box; container: config-block / inline-size; margin: 0; min-width: 240px; min-height: 110px; border: 1px solid var(--ui-border) !important; border-radius: 14px; background: color-mix(in srgb, var(--ui-panel) 94%, var(--ui-accent)) !important; box-shadow: 0 8px 22px color-mix(in srgb, var(--ui-bg) 22%, transparent); overflow: auto; transition: border-color .2s ease, box-shadow .2s ease, opacity .2s ease, transform .2s ease; }
     body[data-card-style="flat"] .config-canvas > .config-block { box-shadow: none; border-radius: 8px; }
@@ -1492,7 +1492,7 @@ HTML = """<!doctype html>
     .network-workspace.has-structure > .network-restore-panel { grid-column: 1; border-right: 1px solid var(--ui-border); border-bottom: 0; }
     .network-workspace.has-structure > .network-canvas { grid-column: 2; }
     .network-restore-panel { min-height: 0; max-height: calc(100vh - 128px); }
-    .network-canvas { position: relative; display: block; min-height: 720px; padding: 14px; overflow: auto; overscroll-behavior: auto; background: radial-gradient(circle at 10% 0%, color-mix(in srgb, var(--ui-accent) 7%, transparent), transparent 32%), color-mix(in srgb, var(--ui-bg) 74%, var(--ui-panel)); }
+    .network-canvas { position: relative; display: block; min-height: max(720px, calc(100dvh - 113px)); padding: 14px; overflow: auto; overscroll-behavior: auto; background: radial-gradient(circle at 10% 0%, color-mix(in srgb, var(--ui-accent) 7%, transparent), transparent 32%), color-mix(in srgb, var(--ui-bg) 74%, var(--ui-panel)); background-color: var(--ui-bg); }
     .network-block { --block-scale: 1; position: absolute; min-width: 240px; min-height: 110px; margin: 0; padding: 14px; border: 1px solid var(--ui-border) !important; border-radius: 14px !important; background: color-mix(in srgb, var(--ui-panel) 94%, var(--ui-accent)) !important; box-shadow: 0 8px 22px color-mix(in srgb, var(--ui-bg) 20%, transparent); overflow: auto; transition: border-color .2s ease, box-shadow .2s ease, transform .2s ease; cursor: grab; touch-action: none; }
     .network-block:hover { border-color: color-mix(in srgb, var(--ui-accent) 48%, var(--ui-border)) !important; transform: translateY(-2px); }
     .network-block.is-selected { border-color: color-mix(in srgb, var(--ui-accent) 70%, var(--ui-border)) !important; box-shadow: 0 0 0 2px color-mix(in srgb, var(--ui-accent) 12%, transparent), 0 8px 22px color-mix(in srgb, var(--ui-bg) 20%, transparent); }