Add interactive WebKit memory watcher script

scripts/memory-test.sh records peak/min WebKit RSS per user-driven
phase (login, global scroll, following scroll, thread open, etc.)
and writes a TSV for side-by-side comparison between builds. Used
during the v0.12.8 OOM investigation and kept for future
regressions. Output files gitignored.

.gitignore

@@ -22,6 +22,9 @@ screenshots/
 *.png
 !src-tauri/icons/*.png
 
+# Memory test output (produced by scripts/memory-test.sh)
+memory-test-*.tsv
+
 # Private docs (drafts, specs, research, grant applications)
 private_docs/
 test/accounts.json