refactor: strip to installer + doctor + docs, remove read/search wrapper layer

BREAKING CHANGE: Remove all `agent-reach read` and `agent-reach search-*` commands.

Agent Reach is now an installer, configuration tool, and doctor —
not a wrapper layer. After installation, agents call upstream tools
directly (bird CLI, yt-dlp, mcporter, gh CLI, Jina Reader, etc.).

What's kept:
- agent-reach install: one-shot installer
- agent-reach doctor: channel status overview
- agent-reach configure: cookies, proxy, credentials
- agent-reach setup: interactive wizard
- SKILL.md: complete guide for agents to use upstream tools directly

What's removed:
- agent-reach read URL (and all channel read() methods)
- agent-reach search-* commands (and all channel search() methods)
- ReadResult / SearchResult data classes
- URL routing system (get_channel_for_url)
- All parsing/conversion logic (VTT, Reddit JSON, bird text parser, etc.)
- MCP server read/search tools (kept only get_status)

Net change: -1790 lines. Less code = fewer bugs.

agent_reach/channels/rss.py

@@ -1,13 +1,7 @@
 # -*- coding: utf-8 -*-
-"""RSS feeds — via feedparser (free, pip dependency).
+"""RSS — check if feedparser is available."""
 
-Backend: feedparser (https://github.com/kurtmckee/feedparser)
-Swap to: any RSS parser
-"""
-
-import feedparser
-from urllib.parse import urlparse
-from .base import Channel, ReadResult
+from .base import Channel
 
 
 class RSSChannel(Channel):
@@ -17,41 +11,11 @@ class RSSChannel(Channel):
     tier = 0
 
     def can_handle(self, url: str) -> bool:
-        lower = url.lower()
-        domain = urlparse(url).netloc.lower()
-        return (lower.endswith(".xml") or "/rss" in lower or "/feed" in lower
-                or "/atom" in lower or "rss" in domain)
+        return any(x in url.lower() for x in ["/feed", "/rss", ".xml", "atom"])
 
-    async def read(self, url: str, config=None) -> ReadResult:
-        feed = feedparser.parse(url)
-
-        if feed.bozo and not feed.entries:
-            raise ValueError(f"Failed to parse RSS feed: {url}")
-
-        if not feed.entries:
-            raise ValueError(f"No entries in RSS feed: {url}")
-
-        # Return latest entry
-        entry = feed.entries[0]
-        content = entry.get("summary", "") or entry.get("description", "")
-
-        # If multiple entries, summarize all
-        if len(feed.entries) > 1:
-            lines = [f"# {feed.feed.get('title', 'RSS Feed')}\n"]
-            for i, e in enumerate(feed.entries[:20], 1):
-                title = e.get("title", "Untitled")
-                link = e.get("link", "")
-                summary = e.get("summary", "")[:200]
-                lines.append(f"## {i}. {title}")
-                lines.append(f"🔗 {link}")
-                if summary:
-                    lines.append(summary)
-                lines.append("")
-            content = "\n".join(lines)
-
-        return ReadResult(
-            title=feed.feed.get("title", entry.get("title", url)),
-            content=content,
-            url=url,
-            platform="rss",
-        )
+    def check(self, config=None):
+        try:
+            import feedparser
+            return "ok", "可读取 RSS/Atom 源"
+        except ImportError:
+            return "off", "feedparser 未安装。安装：pip install feedparser"