Prepare for public release

Add URL/BugReports to DESCRIPTION, fix README license (MIT→GPL-3),
deduplicate .Rbuildignore entry.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: TroyHernandez

DESCRIPTION

@@ -8,6 +8,8 @@ Description: A deterministic, dependency-free documentation generator for R
     using only base R. Supports a strict subset of tags with no markdown parsing,
     no inference magic, and explicit-only behavior.
 License: GPL-3
+URL: https://github.com/cornball-ai/tinyrox
+BugReports: https://github.com/cornball-ai/tinyrox/issues
 Encoding: UTF-8
 Suggests:
     tinytest

README.md

@@ -164,4 +164,4 @@ r -e 'tinyrox::document(); tinypkgr::install(); tinytest::test_package("mypkg")'
 
 ## License
 
-MIT
+GPL-3