feat(core): add SourceResolver for backwards-compatible src/ → source/ migration

Introduces SourceResolver utility class with source/ → src/ → htdocs/
fallback chain, replacing hardcoded src/ references across 28 files.
This enables renaming root-level src/ to source/ in all repos while
maintaining backwards compatibility during the transition.

Phase 1: New lib/Enterprise/SourceResolver.php with resolve(),
resolveAbsolute(), globSource(), findUnderSource(), warnIfLegacy()
Phase 2: Updated 19 CLI/deploy tools to use SourceResolver
Phase 3: Updated 7 validator/lib files (McpServerPlugin,
PackageBuilder, RepositorySynchronizer, auto_detect_platform,
check_dolibarr_module, check_client_theme, check_structure)

Authored-by: Moko Consulting
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/Enterprise/RepositorySynchronizer.php

@@ -1380,7 +1380,7 @@ class RepositorySynchronizer
 
             $descriptors = array_values(array_filter(
                 $paths,
-                static fn(string $p): bool => (bool) preg_match('#src/core/modules/mod\w+\.class\.php$#', $p)
+                static fn(string $p): bool => (bool) preg_match('#(?:source|src)/core/modules/mod\w+\.class\.php$#', $p)
             ));
 
             if (empty($descriptors)) {