chore(ci): replace SourceKnight with setup-sp

[Rushaway]

Summary

Replaces the SourceKnight-based build (maxime1907/action-sourceknight@v1) with a native GitHub Actions CI workflow, following the org-wide migration pattern (using srcdslab/sm-plugin-AdminRoom as the validated reference).

Plugin targets

Target	Source file
ForceInputs	addons/sourcemod/scripting/ForceInputs.sp

Dependencies

Name	Repo URL	Unpack path used
sourcemod	https://sm.alliedmods.net/smdrop/1.11/sourcemod-1.11.0-git6934-linux.tar.gz (tar, not a git dependency)	/addons -> /addons

No type: git dependencies were declared in sourceknight.yaml; the only dependency was the SourceMod tarball itself, which is now provided by rumblefrog/setup-sp (pinned to SourceMod 1.12.x per migration policy) instead of the previously pinned 1.11.0-git6934 tarball.

Changes

• Added .github/workflows/ci.yml modeled on the AdminRoom reference: build job using rumblefrog/setup-sp@v1.3.1 (SourceMod 1.12.x), tag job, and release job (with the corrected actions/checkout@v7 first step in tag and the combined always() && ... condition in release).
• Deleted sourceknight.yaml.
• Updated .github/copilot-instructions.md to remove/replace SourceKnight-specific build instructions with the native spcomp/GitHub Actions equivalents.
• Packaging step copies only addons/sourcemod/plugins/*.smx into the package, since the repo contains no configs/, translations/, or other extra asset directories.

Not locally validated

This migration was performed without cloning dependencies or compiling locally, per the lightweight migration process. GitHub Actions CI on this PR is the source of truth for build correctness.

Manual verification needed

• None identified: the plugin only includes <sourcemod> and <sdktools>, both provided by the base SourceMod install via rumblefrog/setup-sp, with no external dependencies to verify.

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