Fix builtin command ownership classification - #131

What changed

• use the shared ServerFeatures command-ownership registry during builtin command discovery
• exclude ServerFeatures-owned unnamespaced command registrations before Paper/Minecraft wrapper heuristics run
• keep genuine namespaced built-in fallbacks such as minecraft:restart independently blockable
• treat non-Spark PluginIdentifiableCommand implementations as plugin-owned instead of inferring a builtin scope from their namespace
• add regression coverage for ServerFeatures Brigadier commands exposed through vanilla wrappers

Root cause

Paper can expose custom Brigadier roots through vanilla command wrappers / the Minecraft dispatcher. The blocker previously treated wrapper/package/namespace evidence as builtin ownership, so commands such as autopickup, fly, __sfip, and __sfiv could be classified under the minecraft scope when block.minecraft was enabled.

Impact

ServerFeatures commands remain available under their normal labels while genuine Minecraft/Bukkit/Paper/Spigot/Spark built-ins continue to be blocked according to configuration. No command syntax or registration behavior changes.

Validation

• CI Lint: passed
• Maven Verify / Tests and Coverage: passed
• bundled Paper Platform Acceptance: passed
• repository-wide registration audit confirms production Bukkit and Brigadier command registration is routed through FeatureCommandManager
• regression tests cover ServerFeatures-owned vanilla wrappers, namespaced Minecraft fallbacks, and plugin-identifiable ownership precedence