fix: add finance/ to scripts, CI, README, and CONTRIBUTING.md

The finance division (5 agents, PR #431) was merged without updating
the surrounding infrastructure:

- install.sh: added finance to AGENT_DIRS
- convert.sh: added finance to AGENT_DIRS
- lint-agents.sh: added finance to AGENT_DIRS, fixed duplicate sales entry
- lint-agents.yml: added finance/ to CI trigger paths and diff globs
- CONTRIBUTING.md: added finance/ to category list
- README.md: added Finance Division section with all 5 agent entries

scripts/lint-agents.sh

@@ -15,10 +15,10 @@ AGENT_DIRS=(
   academic
   design
   engineering
+  finance
   game-development
   marketing
   paid-media
-  sales
   product
   project-management
   sales