Migrate off third-party SerializeReferenceDropdown to FastTools [TypeSelector]

[VPDPersonal]

Drop the external com.alexeytaranov.serializereferencedropdown dependency and replace [SerializeReferenceDropdown] with Aspid.FastTools [TypeSelector], now that FastTools draws [SerializeReference] fields natively.

Why now

FastTools is already embedded	tech.aspid.fasttools ships with the StarterKit (since #26)
[TypeSelector] now covers [SerializeReference]	VPDPersonal/Aspid.FastTools#49
Removes an external git dependency	one less third-party package to track / pin
Free upgrades	repair, reference graph, open generics, favorites & recents, multi-object edit

The current setup is a versionDefines gate: a local no-op SerializeReferenceDropdownAttribute shim compiles only while the third-party package is absent, otherwise its real attribute + drawer take over. [SerializeReferenceDropdown] is used in ~76 sites across the StarterKit (binders, converters, commands).

Migration steps

#	Change
1	Packages/manifest.json — remove com.alexeytaranov.serializereferencedropdown
2	Aspid.MVVM.StarterKit.asmdef — drop the SerializeReferenceDropdownRuntime reference + the versionDefines entry; reference the FastTools assembly hosting [TypeSelector] instead
3	Replace [SerializeReferenceDropdown] → [TypeSelector] across the ~76 sites
4	Delete the local shim StarterKit/Runtime/Utilities/SerializeReferenceDropdown.cs
5	Regenerate packages-lock.json; update CHANGELOG / MIGRATION (EN + RU)

Risks to verify

• Data round-trips — both attributes sit on plain [SerializeReference] fields, so stored managed-reference data should carry over unchanged; confirm no asset breakage on existing serialized fields.
• Candidate-set parity — FastTools filters Object-derived types, open generics, etc.; check each field still offers the expected implementations, narrowing with [TypeSelector(typeof(Base))] where the old dropdown was broader.
• Graceful absence — the shim used to no-op when the package was missing; after migration [TypeSelector] is always present via the embedded FastTools, so the gate is no longer needed.

Refs

• Feature: SerializeReferenceSelector Aspid.FastTools#10
• Implementation: Add [SerializeReference] dropdown, repair and migration toolkit Aspid.FastTools#49