fix(sync): support Ref-typed properties in live two-way sync

[0hirume]

Companion to argon-rbx/argon#282, which addresses argon-rbx/argon#269 (Ref-typed property sync, e.g. Model.PrimaryPart, Weld.Part0/Part1, ObjectValue.Value).

• Implements Ref and SharedString codecs in EncodedValue (previously stubs that errored), threading a tree reference through encode/decode so Ref values can be resolved to/from instances via Tree:getId/Tree:getInstance.
• Adds Dom.getRefProperties(className) to discover Ref-typed properties via the API database, since they have no DefaultProperties entry and were previously never read.
• Read/Write processors now read and apply Ref-typed properties during live sync.
• stylua --check / selene on changed files
• Manual end-to-end test against the corresponding argon branch: PrimaryPart and Weld Part0/Part1 sync correctly in both directions without crashing