revert: drop PLOTWINDOW forced endpoint snap (#293)

Remove the forces_endpoint_snap mechanism merged in #293:
CadCommand::forces_endpoint_snap, Snapper::snap_forced_corners /
forced_corner_modes, the PlotWindowCommand override, the on_tick +
click-commit wiring, and the associated tests. PLOTWINDOW now uses the
normal snapper like every other command.

Rationale: forcing Endpoint snap on regardless of the global OSNAP master
overrides an explicit user setting and is surprising — a plot window is a
coarse print region that usually wants a margin, not a corner lock, and
the forced set only caught Endpoint (not center/mid/intersection) so it
was a partial, opinionated helper. Parking it pending a design discussion
with the PR author; can be reinstated behind a clearer UX (e.g. respecting
OSNAP, or an opt-in modifier) if justified.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/modules/view/plot_window.rs

@@ -22,10 +22,6 @@ impl CadCommand for PlotWindowCommand {
         "PLOTWINDOW"
     }
 
-    fn forces_endpoint_snap(&self) -> bool {
-        true
-    }
-
     fn prompt(&self) -> String {
         if self.p1.is_none() {
             "PLOTWINDOW  Specify first corner of plot window:".into()
@@ -85,14 +81,3 @@ impl CadCommand for PlotWindowCommand {
 
 // ── Autocomplete registry ─────────────────────────────────
 inventory::submit!(crate::command::CommandRegistration { names: &["PLOTWINDOW", "PW"] });  // PlotWindowCommand
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn plot_window_forces_endpoint_snap() {
-        let cmd = PlotWindowCommand::new();
-        assert!(cmd.forces_endpoint_snap());
-    }
-}