ci(link-check): ignore localhost + skip frozen legacy/archive docs (#404)

The repo-wide link-check on main was red (19 dead links). All were either
local dev-server example URLs or stale references inside frozen historical
docs — not actionable broken links in current content.

- markdown-link-check config: ignore `^https?://localhost` (doc example URLs
  for the dev server: localhost:4001 / :3000 / :3001).
- README.legacy.md (monorepo-era doc, superseded by README.md) and the two
  docs/archive/2026-02 snapshots: add `<!-- markdown-link-check-disable -->` —
  they reference packages/ and planning files that no longer exist and are
  kept only for history.

Verified locally with markdown-link-check against all 6 previously-failing
files: 0 dead links (README.md's 18 real links still checked).

Co-authored-by: Jack Zhuang <277994282+os-zhuang@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: 3 people

.github/markdown-link-check-config.json

@@ -9,6 +9,9 @@
     },
     {
       "pattern": "^https://img.shields.io/"
+    },
+    {
+      "pattern": "^https?://localhost"
     }
   ]
 }

README.legacy.md

@@ -1,3 +1,8 @@
+<!-- markdown-link-check-disable -->
+<!-- Frozen legacy doc from the monorepo era — links point at packages/ and
+     planning files that no longer exist in this single-package repo. Kept for
+     historical reference only; superseded by README.md. -->
+
 # HotCRM - Enterprise-Level CRM System
 
 [![CI](https://github.com/objectstack-ai/hotcrm/workflows/CI/badge.svg)](https://github.com/objectstack-ai/hotcrm/actions/workflows/ci.yml)

docs/archive/2026-02/IMPLEMENTATION_SUMMARY.md

@@ -1,3 +1,7 @@
+<!-- markdown-link-check-disable -->
+<!-- Archived 2026-02 snapshot — references planning docs that have since been
+     removed. Frozen for history; not link-checked. -->
+
 # HotCRM Implementation Complete - Summary
 
 > **Date**: February 11, 2026  

docs/archive/2026-02/SALESFORCE_FEATURE_COMPARISON.md

@@ -1,3 +1,7 @@
+<!-- markdown-link-check-disable -->
+<!-- Archived 2026-02 snapshot — references planning docs that have since been
+     removed. Frozen for history; not link-checked. -->
+
 # HotCRM vs Salesforce: Deep Feature Comparison
 
 > **Version**: 3.0