Add Claude Code support, credential routing polish, and CYA-WP-0006

Mirror sibling-repo Claude setup (CLAUDE.md + .claude/rules/*), align
AGENTS.md with fleet credential-routing template, and close housekeeping
gaps (WP-0002-T05 done, WP-0005 status note). Draft CYA-WP-0006 for
Profile 1 production hardening as the proposed next slice.

CLAUDE.md

@@ -0,0 +1,12 @@
+# can-you-assist — Claude Code Instructions
+
+@SCOPE.md
+@.claude/rules/repo-identity.md
+@.claude/rules/session-protocol.md
+@.claude/rules/first-session.md
+@.claude/rules/workplan-convention.md
+@.claude/rules/stack-and-commands.md
+@.claude/rules/architecture.md
+@.claude/rules/repo-boundary.md
+@.claude/rules/credential-routing.md
+@.claude/rules/agents.md