fix(sessions): Top tools counts each tool call once

The session analysis page's Top tools list counted every event carrying a
tool_name, so each call was counted twice (its PreToolUse and its
PostToolUse) while the Tool calls total beside it counted once — a session
with 840 calls showed Bash at 1,533. The list now counts the same way as
the total: PreToolUse, or PostToolUse in a session with none (imported).

server/db.js

@@ -2547,10 +2547,16 @@ const stmts = {
     FROM events
     WHERE session_id = ? AND tool_name IS NOT NULL
   `),
+  // One row per call, like sessionToolCallTotals: a call is its PreToolUse,
+  // or its PostToolUse in a session that has none (imported). Counting every
+  // event with a tool_name counted each call twice.
   sessionToolUsageCounts: db.prepare(`
     SELECT tool_name, COUNT(*) as count
     FROM events
     WHERE session_id = ? AND tool_name IS NOT NULL
+      AND event_type = CASE
+        WHEN EXISTS (SELECT 1 FROM events WHERE session_id = ? AND event_type = 'PreToolUse')
+        THEN 'PreToolUse' ELSE 'PostToolUse' END
     GROUP BY tool_name
     ORDER BY count DESC
     LIMIT 15