Add Osaurus tool target + document the division contract (#603)

Tooling: add Osaurus (Anthropic Agent-Skills SKILL.md format) as a conversion
and install target, wired into convert.sh (convert_osaurus + dispatch/valid/all/
parallel lists, --osaurus flag) and install.sh (detect/label/dest/install_osaurus
+ dispatch). Generated output lands in integrations/osaurus/agency-*/SKILL.md and
is gitignored like every other tool's output (regenerate via convert.sh osaurus).

Docs/guardrails — make the division contract discoverable, since it lived only
in scattered script comments and tripped up multiple contributors:
- CONTRIBUTING.md: complete the division list to all 16 (was missing academic/
  gis/sales) and document that divisions.json is the source of truth (CI-checked
  by check-divisions.sh), how to propose a new division, and that strategy/
  (NEXUS playbooks) and integrations/ (generated output) are NOT divisions.
- install.sh: correct the stale "sync with convert.sh / lint-agents.sh" comment —
  install.sh intentionally keeps strategy/ in AGENT_DIRS (filtered at scan time),
  so it is deliberately NOT the same set as the other two.
- .gitignore: ignore integrations/osaurus/agency-*/ (the osaurus output was the
  one tool whose generated files weren't excluded).

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -80,3 +80,4 @@ integrations/kimi/*/
 !integrations/openclaw/README.md
 !integrations/kimi/README.md
 integrations/codex/agents/*
+integrations/osaurus/agency-*/