chore(guards): ignore node_modules without a trailing slash and fail on any tracked node_modules path (#627)

.gitignore's `node_modules/` rule matched directories only, so a symlink
named node_modules pointing at a contributor's absolute path was committed
(#623), broke `bun install` in CI with a dangling link and checked out as a
text file on Windows. The rule loses its slash, and security_guards gains a
check that no tracked path has a node_modules component (skipped quietly
outside a git checkout). Also qualifies the one bare `seen_jobs.json`
mention left in README.md after #617.

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

.gitignore

@@ -1,5 +1,5 @@
 # Dependencies
-node_modules/
+node_modules
 bun.lock
 
 # Python
@@ -113,7 +113,7 @@ company_research/*.json
 
 # Agent skills: track the source, ignore only deps and logs.
 # (A blanket `.agents/` ignore silently drops the job-search CLI skills from the repo.)
-.agents/**/node_modules/
+.agents/**/node_modules
 .agents/**/*.log
 .agents/usage/