Sheet sets: Place on Sheet, sheet view menus, block lists, missing status, field refresh

Model Views lists named model views and places them on the current sheet
(xref, viewport, paper-space named view, view label with navigation
fields, sheet view record); sheet view rows get Display, Rename & Renumber
View, Set category, Place Callout Block and Place View Label Block; the
View Category dialog's Add Blocks opens List of Blocks / Select Block; a
sheet whose relative path is gone shows missing; sheet set fields store
their values when a set changes; named views keep their centre relative to
the target. Codec pin moves to the revision with these field helpers.

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

Cargo.toml

@@ -91,7 +91,7 @@ block2 = "0.5"
 objc2-foundation = { version = "0.2", features = ["NSArray", "NSURL", "NSString", "NSObject", "NSNotification", "NSThread", "NSEnumerator"] }
 
 [patch."https://github.com/HakanSeven12/opencadcodec.git"]
-opencadcodec = { git = "https://github.com/ramox81/cadcodec.git", rev = "29aff7e" }
+opencadcodec = { git = "https://github.com/ramox81/cadcodec.git", rev = "1ace49e" }
 
 [patch.crates-io]
 iced_core = { git = "https://github.com/iced-rs/iced.git", rev = "23604ff22ab0aad9e00b9327cb7b8546ed84db39" }