fix: doctor status must be honest — show real capability per channel

Before: everything under tier 0 showed ✅ with vague descriptions
After: each channel shows its actual capability and limitations

Changes:
- GitHub: 'Public repos only. Set github_token for private repos'
- Twitter: shows 'Full access' vs 'Read-only' depending on birdx
- Bilibili: ⚠️ warning on servers about potential IP blocks
- XiaoHongShu: friendly message when no cookie (was showing Jina 451)
- Doctor format: tier 0 items now show detailed status messages, not just ✅
- README: platform table updated to match reality (removed exaggerated claims)
- README: doctor example updated to show new honest format

agent_eyes/channels/twitter.py

@@ -16,7 +16,7 @@ import requests
 
 class TwitterChannel(Channel):
     name = "twitter"
-    description = "Twitter/X posts, search, timelines"
+    description = "Twitter/X posts"
     backends = ["birdx", "Jina Reader"]
     tier = 0  # Single tweet reading is zero-config
 
@@ -27,7 +27,8 @@ class TwitterChannel(Channel):
     def check(self, config=None):
         # Basic reading always works (Jina fallback)
         if shutil.which("birdx"):
-            return "ok", "birdx (full: search + timeline + threads)"
+            return "ok", "Full access (search + timeline + threads)"
+        return "ok", "Read-only (single tweets via Jina). Install birdx for search + timelines"
         return "ok", "Jina Reader (single tweets only)"
 
     async def read(self, url: str, config=None) -> ReadResult: