fix(kyberforge): remove dead plugin-scope branch from validate.sh

check_file()'s is_plugin_scope param and its plugin-silently-ignored
field check were unreachable dead code left over from the issue #89
restructure: plugin/APM scope now exits via check_apm_agent_file()
before check_file() is ever called, so is_plugin was always False.
Remove the param, its branch, the unused plugin_ignored_fields parse,
the now-stale field-inventory.md section, and the SKILL.md mention.

Found via post-implementation review of issue #89.

plugins/kyberforge/skills/agent-audit/scripts/validate.sh

@@ -78,7 +78,6 @@ def parse_section_tokens(content, section_name):
 
 cc_only_fields = parse_section_tokens(inv_content, 'claude-code-only-fields')
 copilot_only_fields = parse_section_tokens(inv_content, 'copilot-only-fields')
-plugin_ignored_fields = parse_section_tokens(inv_content, 'plugin-silently-ignored-fields')
 apm_agent_allowlist = parse_section_tokens(inv_content, 'apm-agent-allowlist')
 
 # Tools the runtime withholds from subagents regardless of the tools field
@@ -239,7 +238,7 @@ else:  # user
         counterpart = os.path.join(home, '.claude', 'agents', name_stem + '.md')
         counterpart_provider = 'claude-code'
 
-def check_file(fpath, file_provider, is_plugin_scope):
+def check_file(fpath, file_provider):
     local_fname = os.path.basename(fpath)
     with open(fpath) as f:
         content = f.read()
@@ -299,13 +298,6 @@ def check_file(fpath, file_provider, is_plugin_scope):
             if key in copilot_only_fields:
                 fail(f"Copilot-only field '{key}' present in CC file — {local_fname}")
 
-    # Silently-ignored fields in plugin-scope CC file
-    if file_provider == 'claude-code' and is_plugin_scope:
-        fm_keys = get_frontmatter_keys(fm)
-        for key in sorted(fm_keys):
-            if key in plugin_ignored_fields:
-                fail(f"plugin-silently-ignored field '{key}' present in plugin-scope CC file — {local_fname}")
-
     # Subagent-unavailable tools listed in tools field
     tools = extract_tools_list(fm)
     unavailable = tools & SUBAGENT_UNAVAILABLE_TOOLS
@@ -318,9 +310,8 @@ if not os.path.isfile(counterpart):
     sys.exit(1)
 
 # --- Check both files ---
-is_plugin = (scope == 'plugin')
-check_file(agent_file, provider, is_plugin)
-check_file(counterpart, counterpart_provider, is_plugin)
+check_file(agent_file, provider)
+check_file(counterpart, counterpart_provider)
 
 for s in suggestions:
     print(f"SUGGESTION  {s}")