chore: gitignore runtime state files (#2075)

* chore: gitignore runtime state files

.claude/scheduled_tasks.lock is a PID+sessionId lock written by Claude
Code's cron scheduler every session. It got accidentally checked in during
the v12.0.0 bump and has been churning phantom diffs in every PR since.
Untrack it and ignore.

plugin/.cli-installed is a timestamp marker the claude-mem installer drops
to record when the plugin was installed. Never belonged in version control.
Ignore it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* chore: add trailing newline to .gitignore

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.claude/scheduled_tasks.lock

@@ -1 +0,0 @@
-{"sessionId":"6a00de6e-282e-4cd8-98ec-b5afb73c468d","pid":50072,"acquiredAt":1775678989779}

.gitignore

@@ -34,7 +34,11 @@ src/ui/viewer.html
 .claude-octopus/
 .claude/session-intent.md
 .claude/session-plan.md
+.claude/scheduled_tasks.lock
 .octo/
 
+# Installer marker — dropped by the claude-mem CLI at install time
+plugin/.cli-installed
+
 # Local contribution analysis (not part of upstream)
-CONTRIB_NOTES.md
+CONTRIB_NOTES.md