docs(docs): add frontmatter to all sprint briefings

Standardized YAML frontmatter on all 115 sprint briefing files across
sprints 1-26 with title, description, type, status, sprint number, and
team fields.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/sprints/sprint-17/server.md

@@ -1,3 +1,12 @@
+---
+title: "Sprint 17 — Server Briefing"
+description: "Knowledge grant architecture, NPC-to-NPC propagation, unprompted disclosure, POI infrastructure"
+type: sprint
+status: archived
+sprint: 17
+team: "server"
+---
+
 # Sprint 17: Tell — Server Tasks
 
 **Goal:** NPCs volunteer information unprompted and express personality through delivery; the knowledge graph becomes a live system with grants, propagation, contradiction detection, and NPC information boundaries; POI infrastructure lands; protocol versioning ships.