feat: add ruleset management for configurable static analysis

Add a comprehensive ruleset management system that allows:
- Enabling/disabling individual rules by ID
- Setting rule severity levels (Off, Info, Warning, Error, Critical)
- Organizing rules by category (Security, DeadCode, Types, WordPress, etc.)
- Predefined rulesets: strict, security, wordpress, minimal, default
- Ruleset merging for inheritance-style configuration
- JSON serialization for loading/saving rulesets

Includes 30+ rule definitions across 7 categories and comprehensive tests.

Author: claude

sanctify-php.cabal

@@ -41,6 +41,7 @@ library
         Sanctify.Emit
         Sanctify.Config
         Sanctify.Report
+        Sanctify.Ruleset
     other-modules:
         Sanctify.Parser.Lexer
         Sanctify.Parser.Token
@@ -96,4 +97,5 @@ test-suite sanctify-php-test
         sanctify-php,
         hspec >=2.10,
         hspec-megaparsec >=2.2,
-        text
+        text,
+        containers