example: split commands into ICommandCategory files (ModSharp/AdminCommands style)

The example module was one ~800-line file. Restructure to match AdminCommands:
- ISpCommandCategory (Register(registry) + optional Unregister())
- ExampleContext — shared deps (SendProxy wrapper accessor, EntityManager,
  ClientManager, ModSharp, Targeting, Logger), the Permission const, Reply(),
  ForceResendAll(), and the parse helpers
- Commands/{Generic,Preset,EncoderDemo,FakeAim,Probe}Commands.cs — one category
  each; FakeAimCommands owns its session state + timer and stops it in Unregister
- ExampleModule slimmed to lifecycle + iterating the category array

No behavior change. Builds 0/0 under TreatWarningsAsErrors.

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