fix(sheetset): wasm build, lock files and sheet set field refresh

- `.dst` read/write go through native-only helpers (a browser answers
  "Not available"); the folder pickers are web no-ops; time stamps use
  iced::time (web-safe).
- Lock files are written only for drawings that are sheets of an open set,
  released when the last set closes, and a lock a crashed session left
  (recorded with its process id, same user and machine) is taken back.
  The `.dwl2` header is well-formed and the date line comes from the OS
  long date on every platform. The 1 Hz poll runs only while a set is open.
- Refreshing sheet set fields never stores `####`: fields no open set
  resolves keep their value, and only the hosts that changed are redrawn
  (and their tab marked modified).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/commands/field.rs

@@ -4,8 +4,8 @@
 use crate::app::{Message, OpenCADStudio};
 use crate::command::CadCommand;
 use crate::modules::annotate::field_cmd::{FieldObjectPickCommand, FieldPlaceCommand, FieldTablePickCommand};
-use crate::ui::window::field_dialog::{nav_props, 
-    fields_of, object_properties, FieldDialogMsg, FieldDialogState, FieldTarget, DATE_FORMATS,
+use crate::ui::window::field_dialog::{
+    fields_of, nav_props, object_properties, FieldDialogMsg, FieldDialogState, FieldTarget, DATE_FORMATS,
     NAMED_TYPES,
 };
 use iced::Task;
@@ -209,7 +209,11 @@ impl OpenCADStudio {
                 state.ss_prop.clear();
             }
             FieldDialogMsg::SsNode(id) => {
-                state.ss_prop = state.ss_sets.get(state.ss_set).and_then(|db| nav_props(db, &id).first().map(|p| p.0.clone())).unwrap_or_default();
+                state.ss_prop = state
+                    .ss_sets
+                    .get(state.ss_set)
+                    .and_then(|db| nav_props(db, &id).first().map(|p| p.0.clone()))
+                    .unwrap_or_default();
                 state.ss_node = id;
             }
             FieldDialogMsg::SsProp(p) => state.ss_prop = p,
@@ -228,10 +232,14 @@ impl OpenCADStudio {
                 );
             }
             FieldDialogMsg::SsPicked(None) => {}
-            FieldDialogMsg::SsPicked(Some(path)) => match codec::sheet_set::SheetSetDatabase::read(&path.to_string_lossy()) {
+            FieldDialogMsg::SsPicked(Some(path)) => match crate::app::commands::sheet_set::read_set(&path.to_string_lossy()) {
                 Ok(db) => {
                     let key = codec::sheet_set::path_key(&path.to_string_lossy());
-                    state.ss_set = match state.ss_sets.iter().position(|d| d.path.as_deref().is_some_and(|p| codec::sheet_set::path_key(p) == key)) {
+                    let open = state
+                        .ss_sets
+                        .iter()
+                        .position(|d| d.path.as_deref().is_some_and(|p| codec::sheet_set::path_key(p) == key));
+                    state.ss_set = match open {
                         Some(k) => k,
                         None => {
                             state.ss_sets.push(db);