fix: prune dead web_search tool — ddgs never installed (#87)

Remove DuckDuckGoTools import, all web_search registrations across 4 toolkit
factories, catalog entry, safety classification, prompt references, and
session regex. Total: -41 lines of dead code.

consult_grok is functional (grok_enabled=True, API key set) and opt-in,
so it stays — but Timmy never calls it autonomously, which is correct
sovereign behavior (no cloud calls unless user permits).

Closes #87

src/timmy/tool_safety.py

@@ -37,7 +37,6 @@ DANGEROUS_TOOLS = frozenset(
 # Tools that are safe to execute without confirmation.
 SAFE_TOOLS = frozenset(
     {
-        "web_search",
         "calculator",
         "memory_search",
         "memory_read",