Update .gitignore to ignore generated documentation, coverage reports, performance logs, and macOS files

Author: d-oit

.gitignore

@@ -38,3 +38,21 @@ dev-workflow.log
 opencodetmp/opencode
 opencodetmp/opencode-linux-x64.zip
 sccache-*-musl/
+
+# Additional ignores
+
+# Generated documentation (mdbook output)
+docs/book/
+
+# Coverage reports
+coverage/
+html/
+coverage-report/
+*.lcov
+coverage.lcov
+
+# Performance monitoring logs and state
+performance/
+
+# macOS
+.DS_Store