Drop strategy/ as a division — it's playbooks/runbooks, not agents (#595)

strategy/ holds 16 markdown files and ZERO have agent frontmatter — they're
playbooks (playbooks/phase-*.md), runbooks (runbooks/scenario-*.md), and briefs
(EXECUTIVE-BRIEF.md, QUICKSTART.md, nexus-strategy.md), not agent definitions.
There are 16 real agent divisions, 232 agents; strategy is not one of them.

#592 added `strategy` to lint-agents.sh AGENT_DIRS and the lint workflow paths
(to match divisions.json), which made CI lint those 16 frontmatter-less docs as
agents and fail every one with "missing frontmatter opening ---". So any PR
touching strategy/ broke CI. The original lint-agents.sh correctly excluded
strategy; #592 misread that deliberate exclusion as drift (same mistake as
integrations/ in #593).

Fix: remove strategy from convert.sh / lint-agents.sh AGENT_DIRS, the lint
workflow, and divisions.json; add it to NON_DIVISION_DIRS in check-divisions.sh.
divisions.json is now 16, matching the app's parse_agent count exactly.

Also add a content-derived backstop to check-divisions.sh: every division must
contain at least one .md with '---' frontmatter, or the build fails. This is
what stops a docs/playbook directory from being registered as an empty agent
division again — regardless of whether someone remembers the exclude list.

check-divisions.sh PASSES at 16; negative-tested that re-adding strategy fails
with "division 'strategy' has no agent files".

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

scripts/convert.sh

@@ -68,7 +68,7 @@ TODAY="$(date +%Y-%m-%d)"
 
 AGENT_DIRS=(
   academic design engineering finance game-development gis marketing paid-media product project-management
-  sales security spatial-computing specialized strategy support testing
+  sales security spatial-computing specialized support testing
 )
 
 # --- Usage ---