v2.0.0 — Pure glue architecture: zero copied code, pluggable channels

BREAKING: Complete architectural rewrite.

Before: Copied x-reader's fetcher code into readers/ (1205 lines of borrowed code)
After: Pluggable channel system where each channel is a thin wrapper (~50 lines)
       around the best external tool for that platform. Zero copied code.

Architecture:
- channels/base.py — Universal Channel interface (read, search, check)
- channels/web.py — Jina Reader API (swappable)
- channels/github.py — GitHub API (swappable)
- channels/twitter.py — birdx + Jina fallback (swappable)
- channels/youtube.py — yt-dlp (swappable)
- channels/reddit.py — Reddit JSON API + proxy (swappable)
- channels/rss.py — feedparser (swappable)
- channels/bilibili.py — Bilibili API (swappable)
- channels/exa_search.py — Exa semantic search (swappable)

Key design: every backend can be swapped by changing ONE file.
YouTube dies? Change youtube.py. Exa sucks? Swap exa_search.py for Tavily.
Nothing else changes.

Removed: reader.py, schema.py, readers/, search/, utils/ (all x-reader code)
Tests: 36/36 passing

agent_eyes/channels/exa_search.py

@@ -0,0 +1,69 @@
+# -*- coding: utf-8 -*-
+"""Exa semantic search — the search backbone for Agent Eyes.
+
+Backend: Exa API (https://exa.ai) — free 1000 searches/month
+Swap to: Tavily, SerpAPI, or any search API
+"""
+
+import os
+import requests
+from .base import Channel, SearchResult
+from typing import List
+
+
+class ExaSearchChannel(Channel):
+    name = "exa_search"
+    description = "Semantic web search (powers Reddit/Twitter search too)"
+    backends = ["Exa API"]
+    requires_config = ["exa_api_key"]
+    tier = 1
+
+    API_URL = "https://api.exa.ai/search"
+
+    def can_handle(self, url: str) -> bool:
+        return False  # Search-only channel, doesn't read URLs
+
+    async def read(self, url: str, config=None) -> None:
+        raise NotImplementedError("Exa is a search engine, not a reader")
+
+    def _get_key(self, config=None) -> str:
+        if config:
+            key = config.get("exa_api_key")
+            if key:
+                return key
+        key = os.environ.get("EXA_API_KEY")
+        if key:
+            return key
+        raise ValueError(
+            "Exa API key not configured.\n"
+            "Get a free key at https://exa.ai (1000 searches/month free)\n"
+            "Then run: agent-eyes setup"
+        )
+
+    async def search(self, query: str, config=None, **kwargs) -> List[SearchResult]:
+        api_key = self._get_key(config)
+        limit = kwargs.get("limit", 5)
+
+        resp = requests.post(
+            self.API_URL,
+            headers={"Content-Type": "application/json", "x-api-key": api_key},
+            json={
+                "query": query,
+                "numResults": min(limit, 10),
+                "type": "auto",
+                "contents": {"text": {"maxCharacters": 500}},
+            },
+            timeout=15,
+        )
+        resp.raise_for_status()
+
+        results = []
+        for item in resp.json().get("results", []):
+            results.append(SearchResult(
+                title=item.get("title", ""),
+                url=item.get("url", ""),
+                snippet=item.get("text", ""),
+                date=item.get("publishedDate", ""),
+                score=item.get("score", 0),
+            ))
+        return results