isokit: web Studio (engine as WASM, projects in the browser or a live folder)

- isokit-wasm: wasm-bindgen build of the engine; a project in memory behind
  the same JSON API as `isokit studio`, plus the MCP tools
- isokit-project: Store trait (FsStore folder, MemStore memory) under a
  generic Workspace; Project::from_files; shared Studio API module (api.rs)
  used by serve.rs and the WASM build; web_time for clocks in the browser
- studio.js runs on a pluggable backend (window.IsoKitBackend); no Studio
  keys while a dialog is open
- web/: projects in IndexedDB, new/demo/delete, zip export/import (stored and
  deflated), folder import by drop or picker, folders opened live via File
  System Access with outside edits followed, code editor, page build and
  preview, two tabs in step, isokit.mcp() and WebMCP registration
- tools/build_web.py -> dist/web (static), tools/check_web.py (44 checks)

web/web.css

@@ -0,0 +1,42 @@
+/* isokit web Studio: the parts the desktop Studio does not have (projects, code editor). */
+.wb-where { color: var(--mute); font-size: 12px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; max-width: 180px; }
+
+.wb-projdlg { width: min(660px, 94vw); max-width: none; }
+.wb-projdlg h3 { margin: 0 0 10px; }
+.wb-cur { display: flex; align-items: center; gap: 8px; padding: 6px 8px; background: var(--panel2); border-radius: 6px; margin-bottom: 10px; }
+.wb-cur small { color: var(--mute); }
+.wb-plist { list-style: none; margin: 0 0 10px; padding: 0; max-height: 40vh; overflow: auto; border: 1px solid var(--stroke); border-radius: 6px; }
+.wb-plist li { display: flex; align-items: center; gap: 8px; padding: 4px 8px; border-bottom: 1px solid var(--stroke); }
+.wb-plist li:last-child { border-bottom: 0; }
+.wb-plist li[aria-current=true] { background: color-mix(in srgb, var(--accent) 14%, var(--panel)); }
+.wb-plist li i { font-style: normal; width: 18px; text-align: center; }
+.wb-plist li span { flex: 1 1 auto; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+.wb-plist li small { color: var(--mute); white-space: nowrap; }
+.wb-plist li button { padding: 2px 8px; }
+.wb-plist .wb-empty { color: var(--mute); }
+.wb-new { display: flex; gap: 6px; margin-bottom: 8px; }
+.wb-new input { flex: 1 1 auto; }
+/* one compact line: drop target and pickers together */
+.wb-drop { border: 1px dashed var(--stroke); border-radius: 6px; padding: 6px 8px; color: var(--mute); display: flex; flex-wrap: wrap; align-items: center; gap: 4px 6px; }
+.wb-drop button { padding: 1px 8px; }
+.wb-drop.wb-over { border-color: var(--accent); background: color-mix(in srgb, var(--accent) 12%, var(--panel)); color: var(--fg); }
+.wb-projdlg .st-help { margin: 8px 0 0; }
+
+.wb-codedlg { width: min(1180px, 96vw); max-width: none; height: min(820px, 90vh); padding: 0; display: none; flex-direction: column; overflow: hidden; }
+.wb-codedlg[open] { display: flex; }
+.wb-chead { display: flex; align-items: center; gap: 6px; padding: 8px 10px; border-bottom: 1px solid var(--stroke); }
+.wb-cpath { color: var(--mute); font-family: ui-monospace, Consolas, monospace; font-size: 12px; margin-left: 6px; }
+.wb-cbody { flex: 1 1 auto; display: grid; grid-template-columns: 200px minmax(0, 1fr); min-height: 0; }
+.wb-cfiles { list-style: none; margin: 0; padding: 6px; overflow: auto; border-right: 1px solid var(--stroke); font-family: ui-monospace, Consolas, monospace; font-size: 12px; }
+.wb-cfiles li { padding: 3px 6px; border-radius: 4px; cursor: pointer; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
+.wb-cfiles li:hover { background: var(--panel2); }
+.wb-cfiles li[aria-selected=true] { background: color-mix(in srgb, var(--accent) 20%, var(--panel)); }
+.wb-cbody textarea { border: 0; border-radius: 0; resize: none; padding: 10px 12px; font: 12.5px/1.5 ui-monospace, "Cascadia Code", Consolas, monospace; tab-size: 2; white-space: pre; overflow: auto; background: var(--bg); }
+.wb-cmsg { padding: 6px 10px; border-top: 1px solid var(--stroke); color: var(--mute); font: 12px/1.4 ui-monospace, Consolas, monospace; white-space: pre-wrap; max-height: 9em; overflow: auto; }
+.wb-cmsg.wb-bad { color: var(--danger); }
+
+.wb-gate[hidden] { display: none; }
+.wb-gate { position: fixed; inset: 0; z-index: 40; background: color-mix(in srgb, var(--bg) 82%, transparent); display: flex; align-items: center; justify-content: center; }
+.wb-gatebox { background: var(--panel); border: 1px solid var(--stroke); border-radius: 8px; padding: 16px 18px; max-width: min(620px, 92vw); }
+.wb-gatebox h3 { margin: 0 0 8px; }
+.wb-gatebox pre { white-space: pre-wrap; color: var(--danger); font-size: 12px; max-height: 40vh; overflow: auto; }