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-20/client.md

@@ -1,3 +1,12 @@
+---
+title: "Sprint 20 — Client Briefing"
+description: "Refactor game_state, dialogue_box, main.gd coordinator, unify YAML parsers"
+type: sprint
+status: archived
+sprint: 20
+team: "client"
+---
+
 # Sprint 20: Shape — Client Tasks
 
 **Goal:** The social site template system gains its foundational schema; triangles become generatable and observable as escalating tensions; the client gains save/load UI and code quality improvements.

docs/sprints/sprint-20/joint.md

@@ -1,3 +1,12 @@
+---
+title: "Sprint 20 — Joint Briefing"
+description: "Triangle configuration, social site schema, client refactor coordination"
+type: sprint
+status: archived
+sprint: 20
+team: "joint"
+---
+
 # Sprint 20: Shape — Joint Coordination
 
 **Goal:** The social site template system gains its foundational schema; triangles become generatable and observable as escalating tensions; the client gains save/load UI and code quality improvements.

docs/sprints/sprint-20/planning.md

@@ -1,3 +1,12 @@
+---
+title: "Sprint 20 — Planning Briefing"
+description: "Station district layout design discussion, D-record production"
+type: sprint
+status: archived
+sprint: 20
+team: "planning"
+---
+
 # Sprint 20: Shape — Planning Tasks
 
 **Goal:** Resolve the station district layout design through structured discussion, producing a confirmed D-record that unblocks Sprint 21 location authoring and triangle instantiation.

docs/sprints/sprint-20/server.md

@@ -1,3 +1,12 @@
+---
+title: "Sprint 20 — Server Briefing"
+description: "Role definition schema, spatial requirements, triangle definition and generation"
+type: sprint
+status: archived
+sprint: 20
+team: "server"
+---
+
 # Sprint 20: Shape — Server Tasks
 
 **Goal:** The social site template system gains its foundational schema; triangles become generatable and observable as escalating tensions; the client gains save/load UI and code quality improvements.