licence,ci: ship OFL with Plex fonts and guard release dispatch (P5)

IBM Plex WOFF2 files were shipped without the SIL OFL 1.1 text, NOTICE
told modifiers to edit layout.html for a Source URL that lives in
legal.go, and workflow_dispatch took GITHUB_REF_NAME as the version so a
run from main would publish ghcr.io/...:main.

Closes P5 of docs/plans/code-review.md. CHANGELOG updated.

Co-Authored-By: Cursor Grok 4.6 <noreply@anthropic.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

internal/legal/legal.go

@@ -14,8 +14,9 @@ import (
 var License []byte
 
 // SourceURL is where Corresponding Source for the published upstream
-// releases lives. Operators who ship a modified version must point their
-// users at their own sources instead (NOTICE; AGPL-3.0 §13).
+// releases lives. It is injected into the panel footer by view.go.
+// Operators who ship a modified version must change this constant so the
+// footer points at their own sources (NOTICE; AGPL-3.0 §13).
 const SourceURL = "https://github.com/mixeme/selfpost"
 
 // CopyrightLine is the short copyright notice shown in the panel footer.