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>

cli/theme_lint.php

@@ -17,7 +17,7 @@ declare(strict_types=1);
 
 require_once __DIR__ . '/../lib/Enterprise/CliFramework.php';
 
-use MokoEnterprise\CliFramework;
+use MokoEnterprise\{CliFramework, SourceResolver};
 
 class ThemeLintCli extends CliFramework
 {
@@ -41,17 +41,12 @@ class ThemeLintCli extends CliFramework
         $errors = 0;
         $warnings = 0;
 
-        $srcDir = null;
-        foreach (['src', 'htdocs'] as $d) {
-            if (is_dir("{$root}/{$d}")) {
-                $srcDir = "{$root}/{$d}";
-                break;
-            }
-        }
+        $srcDir = SourceResolver::resolveAbsolute($root);
         if ($srcDir === null) {
-            $this->log('ERROR', "No src/ or htdocs/ directory in {$root}");
+            $this->log('ERROR', "No source/ or src/ directory in {$root}");
             return 1;
         }
+        SourceResolver::warnIfLegacy($root);
 
         echo "Theme Lint: {$srcDir}\n\n";