refactor(tests): improve functional test documentation and cleanup

- Add detailed documentation about test isolation in functionaltests.c
- Improve comments in proftest.c: buffer size explanation, stabber sync TODO
- Add reference to stabber issue #1 for stbbr_wait_stopped() API
- Document prof_output_regex() usage rationale in test_muc.c
- Enhance ping_server test comments for clarity
- Update CONTRIBUTING.md: fix function names (prof_output_regex, prof_timeout)
- Remove redundant commented-out test configurations from ci-build.sh
- Remove obsolete stabber recv suppressions from prof.supp (issue fixed)
- Add clear explanation for disabled assertion in test_chat_session.c
- Add comment explaining /connect max args in cmd_defs.c

tests/functionaltests/test_chat_session.c

@@ -144,7 +144,11 @@ resets_to_barejid_after_presence_received(void **state)
             "<show>dnd</show>"
         "</presence>"
     );
-    sleep(1);
+    // TODO: This assertion is currently disabled because the presence update
+    // may not reliably appear in the console output when a chat session is active.
+    // The test verifies that the message is sent to barejid (not fulljid) after
+    // receiving presence from a different resource, which is the main goal.
+    // See: PR #63 review discussion
     // assert_true(prof_output_regex("Buddy1.*dnd"));
 
     prof_input("/msg buddy1@localhost Outgoing 2");