chore(ci): replace SourceKnight with setup-sp

[Rushaway]

Summary

Replaces the SourceKnight-based build (maxime1907/action-sourceknight@v1) with a native GitHub Actions workflow using rumblefrog/setup-sp and spcomp, following the org-wide rollout pattern (see srcdslab/sm-plugin-AdminRoom as the validated reference).

Plugin targets

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

Dependencies (from sourceknight.yaml)

Name	Repo	Unpack source → dest (as declared)
multicolors	https://github.com/srcdslab/sm-plugin-MultiColors	/addons → /addons
SelfMute	https://github.com/srcdslab/sm-plugin-SelfMute	/addons → /addons
sourcebans-pp	https://github.com/srcdslab/sourcebans-pp	/game/addons → /addons
dynamicchannels	https://github.com/Vauff/DynamicChannels	/scripting/include → /addons/sourcemod/scripting/include

(sourcemod type: tar runtime dependency omitted from the table above — it is now provided by rumblefrog/setup-sp instead, pinned to 1.12.x per the org-wide migration standard, regardless of the version previously pinned in sourceknight.yaml.)

Packaging

The new workflow packages the compiled .smx plus addons/sourcemod/configs and addons/sourcemod/translations, both of which exist in this repo tree (mirroring what the old SourceKnight-based workflow copied into the package).

Not locally validated

This is a lightweight migration pass: no dependency repos were cloned locally, no spcomp was run, and no local compilation was performed. The workflow's correctness (dependency include paths, compile success, packaging) relies entirely on the GitHub Actions CI run triggered by this PR. Please review the CI results before merging.

Manual verification needed

• The dependency include paths above were carried over as declared in sourceknight.yaml without independently verifying the internal directory layout of each dependency repo. If CI fails on a missing include, the most likely culprit is a mismatched unpack path for one of multicolors, SelfMute, sourcebans-pp, or dynamicchannels.
• This repo also has csgo-legacy and new-multicolors branches that were not migrated by this PR (only master, the default branch, was touched).

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