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/__init__.py

@@ -1,14 +1,10 @@
 # -*- coding: utf-8 -*-
 """
-Channel registry — routes URLs to the right channel.
-
-This is the core of Agent Reach' pluggable architecture.
-Add a new channel: just create a file and register it here.
-Swap a backend: just change the implementation inside the channel file.
+Channel registry — lists all supported platforms for doctor checks.
 """
 
-from typing import Dict, List, Optional
-from .base import Channel, ReadResult, SearchResult
+from typing import List, Optional
+from .base import Channel
 
 # Import all channels
 from .web import WebChannel
@@ -24,7 +20,7 @@ from .linkedin import LinkedInChannel
 from .bosszhipin import BossZhipinChannel
 
 
-# Channel registry — order matters (first match wins, web is last as fallback)
+# Channel registry
 ALL_CHANNELS: List[Channel] = [
     GitHubChannel(),
     TwitterChannel(),
@@ -36,22 +32,9 @@ ALL_CHANNELS: List[Channel] = [
     BossZhipinChannel(),
     RSSChannel(),
     ExaSearchChannel(),
-    WebChannel(),        # Fallback — handles any URL
+    WebChannel(),
 ]
 
-# Search-capable channels
-SEARCH_CHANNELS: Dict[str, Channel] = {
-    ch.name: ch for ch in ALL_CHANNELS if ch.can_search()
-}
-
-
-def get_channel_for_url(url: str) -> Channel:
-    """Find the right channel for a URL."""
-    for channel in ALL_CHANNELS:
-        if channel.can_handle(url):
-            return channel
-    return WebChannel()  # Should never reach here, but just in case
-
 
 def get_channel(name: str) -> Optional[Channel]:
     """Get a channel by name."""
@@ -67,7 +50,7 @@ def get_all_channels() -> List[Channel]:
 
 
 __all__ = [
-    "Channel", "ReadResult", "SearchResult",
-    "ALL_CHANNELS", "SEARCH_CHANNELS",
-    "get_channel_for_url", "get_channel", "get_all_channels",
+    "Channel",
+    "ALL_CHANNELS",
+    "get_channel", "get_all_channels",
 ]