fix: nullish coalescing in evaluate-session config, narrow pre-compact glob, add 11 tests

- evaluate-session.js: || 10 → ?? 10 for min_session_length (0 is valid)
- pre-compact.js: *.tmp → *-session.tmp to match only session files
- 11 new tests: config loading (min=0, null, custom path, invalid JSON),
  session-end update path (timestamp, template replace, preserve content),
  pre-compact glob specificity, extractSessionSummary edge cases

scripts/hooks/evaluate-session.js

@@ -64,7 +64,7 @@ async function main() {
   if (configContent) {
     try {
       const config = JSON.parse(configContent);
-      minSessionLength = config.min_session_length || 10;
+      minSessionLength = config.min_session_length ?? 10;
 
       if (config.learned_skills_path) {
         // Handle ~ in path