feat(automation): entity, block, publishing and REST operations from the fork

The operations docs/automation/API-SPEC.md (PR #1383) describes, brought
over from huaninstratech/OpenCADStudio so the specification no longer runs
ahead of the code:

- entity CRUD: entities_create, entities_delete, entities_transform,
  entities_copy_to, and `where` filters on query
- blocks and export: block_define, block_delete, a normalised wblock
- publishing: layout_create, page_setup_set, plot (per_page included)
- metadata: sysvar, xdata_set / xdata_get, file_identity
- collections: group_create, selection_set_save / load
- control plane: batch, events, view_focus, close
- the REST transport: `--http <port>`, the /api/v1 routes and their
  OpenAPI 3 description
- person-in-the-loop picks: user_select and getpoint, hosted by the GUI
  over the same REST routes, with on-screen pending signals

Taken from the fork's commits b7a7ed80, 69396b42, 64f1cf6a, c3aafc8e,
bb5a7bfa, 52317a5c, 50d293ba, b90e194f, 517c6397, 53a5c4c9, a49ac045,
37de5a46, a78b1822, 6d9aed2a, 33f522da, 5b5cafe2, 02a7e78d, 94df40dc,
fd5bc14d, 485fac61 and 2c5fc994.

Left out on purpose: 37de5a46 also removed the donation surface (the
Patreon fetch, the donation prompt, the Start-page supporters rail, the
DONATE command and its locale strings) and replaced the About dialog's call
to action; that is the fork's own product decision and stays out. The
fork's version bump and its unrelated IFC/BIM work are not part of this.

Adapted while porting: the REST server and the GUI bridge are desktop-only
and a template start is refused in the web build, so the wasm target still
compiles; the two plot tests read the PDF through the shared stream helper,
because exported streams are Flate-compressed; the benches set the new
crosshair field; comments and docs describe each operation in its own
terms rather than by another product's API names.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/cli.rs

@@ -85,6 +85,11 @@ pub struct Cli {
     #[arg(help = crate::t!("TCP port for --serve (defaults to stdin/stdout).").into_owned(), long_help = None)]
     pub port: Option<u16>,
 
+    /// Expose the headless automation API as a REST HTTP server on this port.
+    #[arg(long, value_name = "PORT")]
+    #[arg(help = crate::t!("Serve the automation API over REST on http://127.0.0.1:PORT").into_owned(), long_help = None)]
+    pub http: Option<u16>,
+
     /// Headless convert: read IN, write OUT (format from OUT's extension), exit.
     #[arg(long, num_args = 2, value_names = ["IN", "OUT"])]
     #[arg(help = crate::t!("Convert IN to OUT using the output file extension, then exit.").into_owned(), long_help = None)]