feat: in-place save (File System Access), image paste, print wiring, web capture

The last high-severity web gap plus a small integration bundle.

In-place save: with the File System Access API (Chromium/Edge), Save
now works like desktop. Plain Save on a tab with a retained handle
writes straight through — no picker, no download, no "(1)" copies.
First save or format change opens showSaveFilePicker AT the confirm
gesture (the worker serialization that follows can outlast the
transient-activation window; retained handles need no activation to
write). Picker cancel cancels the save like desktop; picker or write
failure falls back to the legacy download with a note; Firefox/Safari
keep the download flow untouched (feature-detected). Handles are
keyed by tab id in a thread-local registry (Message must be Send —
JsValue cannot ride in messages or App state); closing a tab drops
its handle; Save As re-picks. Dirty clears only on successful
persistence, same race guard as before.

Image paste: Ctrl+V of a screenshot inserts it as an image reference
— the clipboard reader falls back to image/* items when neither the
entity clipboard nor text has anything (precedence preserved), the
bytes enter the image source registry as pasted-<timestamp>.<ext>,
and attach reuses the IMAGE command's model-creation path verbatim.

Browser print: beforeprint snapshots the WebGL canvas into a print-
only <img> (the capture_canvas technique), so the browser's own print
menu produces the drawing instead of a blank page.

Automation capture on web: the capture op no longer calls the
synchronous GPU-map screenshot (dead on wasm); it waits one presented
frame and reads via capture_canvas — the same workaround the save-
thumbnail path uses — delivering the PNG as a download.

Cargo.toml

@@ -122,6 +122,9 @@ web-sys = { version = "=0.3.85", features = [
     "File",
     "FileSystemDirectoryHandle",
     "FileSystemFileHandle",
+    # FileSystemFileHandle derefs to FileSystemHandle for the `name()`
+    # getter the in-place save (io::fs_access) reads off a picked handle.
+    "FileSystemHandle",
     "FileSystemGetDirectoryOptions",
     "FileSystemGetFileOptions",
     "FileSystemWritableFileStream",
@@ -144,6 +147,10 @@ web-sys = { version = "=0.3.85", features = [
     "MessageEvent",
     "ErrorEvent",
     "Clipboard",
+    # The web image paste reads `navigator.clipboard.read()` items
+    # (sys::read_clipboard_image): their `types()`/`getType()` surface lives
+    # on ClipboardItem.
+    "ClipboardItem",
     "KeyboardEvent",
     "KeyboardEventInit",
     "EventInit",