Use real journal filtering in session_end scans

[zhuhaoxiang1]

session_end has several direct .md scans over the project journal directory:

• duplicate ## Brief detection for same-day saves
• recent-entry merge suggestion scanning
• save-card journal count rendering

Other session/project board paths already use isJournalFile() to exclude capture logs, weekly rollups, merged files, and index.md. session_end should use the same filter so auxiliary journal files do not count as real session entries or affect same-day save behavior.

I can send a small tested PR that reuses isJournalFile() in session_end and adds a regression test for same-day capture logs.