improve search_code query parameter description

The current `query` description for `search_code` gives the model little
useful guidance on GitHub code search syntax, leading to repeated
422 ERROR_TYPE_QUERY_PARSING_FATAL responses from agents that guess at
plausible-looking but invalid syntax (e.g. regex without slashes,
`filename:` instead of `path:`, `OR` between qualifiers without parentheses).

Replace the description with one that explicitly enumerates qualifiers,
boolean operators, regex form (slashes), and path globs, plus realistic
examples covering each.

Updates the search_code toolsnap and README accordingly.

Fixes #2390.

Author: jluocsa

README.md

@@ -1276,7 +1276,7 @@ The following sets of tools are available:
   - `order`: Sort order for results (string, optional)
   - `page`: Page number for pagination (min 1) (number, optional)
   - `perPage`: Results per page for pagination (min 1, max 100) (number, optional)
-  - `query`: Search query using GitHub's powerful code search syntax. Examples: 'content:Skill language:Java org:github', 'NOT is:archived language:Python OR language:go', 'repo:github/github-mcp-server'. Supports exact matching, language filters, path filters, and more. (string, required)
+  - `query`: Search query using GitHub code search syntax. Qualifiers: repo:owner/repo, org:name, language:Go, path:src/*.js, path:/regex/, symbol:Name, content:term, is:archived|fork. Boolean: AND, OR, NOT, parentheses. Regex: surround with slashes e.g. /sparse.*index/. Glob in path: path:*.ts, path:/src/**/*.js. Examples: 'MyFunc language:go repo:owner/repo', 'symbol:WithContext language:go', '/GetAttributes|SetAttributes/ repo:owner/repo', '(Foo OR Bar) path:src repo:owner/repo'. (string, required)
   - `sort`: Sort field ('indexed' only) (string, optional)
 
 - **search_repositories** - Search repositories

pkg/github/__toolsnaps__/search_code.snap

@@ -26,7 +26,7 @@
         "type": "number"
       },
       "query": {
-        "description": "Search query using GitHub's powerful code search syntax. Examples: 'content:Skill language:Java org:github', 'NOT is:archived language:Python OR language:go', 'repo:github/github-mcp-server'. Supports exact matching, language filters, path filters, and more.",
+        "description": "Search query using GitHub code search syntax. Qualifiers: repo:owner/repo, org:name, language:Go, path:src/*.js, path:/regex/, symbol:Name, content:term, is:archived|fork. Boolean: AND, OR, NOT, parentheses. Regex: surround with slashes e.g. /sparse.*index/. Glob in path: path:*.ts, path:/src/**/*.js. Examples: 'MyFunc language:go repo:owner/repo', 'symbol:WithContext language:go', '/GetAttributes|SetAttributes/ repo:owner/repo', '(Foo OR Bar) path:src repo:owner/repo'.",
         "type": "string"
       },
       "sort": {

pkg/github/search.go

@@ -173,7 +173,7 @@ func SearchCode(t translations.TranslationHelperFunc) inventory.ServerTool {
 		Properties: map[string]*jsonschema.Schema{
 			"query": {
 				Type:        "string",
-				Description: "Search query using GitHub's powerful code search syntax. Examples: 'content:Skill language:Java org:github', 'NOT is:archived language:Python OR language:go', 'repo:github/github-mcp-server'. Supports exact matching, language filters, path filters, and more.",
+				Description: "Search query using GitHub code search syntax. Qualifiers: repo:owner/repo, org:name, language:Go, path:src/*.js, path:/regex/, symbol:Name, content:term, is:archived|fork. Boolean: AND, OR, NOT, parentheses. Regex: surround with slashes e.g. /sparse.*index/. Glob in path: path:*.ts, path:/src/**/*.js. Examples: 'MyFunc language:go repo:owner/repo', 'symbol:WithContext language:go', '/GetAttributes|SetAttributes/ repo:owner/repo', '(Foo OR Bar) path:src repo:owner/repo'.",
 			},
 			"sort": {
 				Type:        "string",