Add web_search / web_fetch tools for pi-harness agents

pi ships no web tools and claude's WebSearch/WebFetch are Anthropic-server-side
(absent on local endpoints), so these are handler-owned: a new handler.webtool
module (httpx, already a dependency) exposed through the bridge extension the
same way as the memory tools. web_fetch is provider-free — GET, HTML stripped
to readable text, size-capped. web_search resolves SEARXNG_URL, then
BRAVE_SEARCH_API_KEY, then falls back to DuckDuckGo's HTML endpoint with zero
config. Verified live: a pi agent now advertises all 14 tools (7 built-ins +
ask_operator + 4 memory + 2 web).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KdGv3u3DfTsP1S188KDhVH

tests/test_pi_harness.py

@@ -107,8 +107,10 @@ def test_write_config_renders_provider_and_bridge(pi_env, tmp_path):
     assert "handler.mcpserver" in text
     assert "ask_operator" in text
     # Tool parity: the bridge activates pi's full built-in set (grep/find/ls are off
-    # by default) alongside its own tools.
+    # by default) alongside its own tools, and registers the handler web tools.
     assert "setActiveTools" in text
+    assert "handler.webtool" in text
+    assert "web_search" in text and "web_fetch" in text
     assert (base / "APPEND_SYSTEM.md").read_text().strip()