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-9/audio.md

@@ -1,3 +1,12 @@
+---
+title: "Sprint 9 — Audio Briefing"
+description: "Interaction audio assets completion, Sprint 7 UI audio asset revision"
+type: sprint
+status: archived
+sprint: 9
+team: "audio"
+---
+
 # Sprint 9: Gauntlet — Audio Tasks
 
 **Goal:** Build the test infrastructure backbone — test client binary, Gauntlet rooms 1-3, golden file suite, and client QA harness — so every future sprint can be validated end-to-end.

docs/sprints/sprint-9/ci.md

@@ -1,3 +1,12 @@
+---
+title: "Sprint 9 — CI Briefing"
+description: "make pre-pr target, content cross-reference validation, fixture staleness check"
+type: sprint
+status: archived
+sprint: 9
+team: "ci"
+---
+
 # Sprint 9: Gauntlet — CI Tasks
 
 **Goal:** Build the test infrastructure backbone — test client binary, Gauntlet rooms 1-3, golden file suite, and client QA harness — so every future sprint can be validated end-to-end.

docs/sprints/sprint-9/client.md

@@ -1,3 +1,12 @@
+---
+title: "Sprint 9 — Client Briefing"
+description: "Client P2/P3 Gauntlet tests, WRONG button MVP, room timer, MessagePack fix"
+type: sprint
+status: archived
+sprint: 9
+team: "client"
+---
+
 # Sprint 9: Gauntlet — Client Tasks
 
 **Goal:** Build the test infrastructure backbone — test client binary, Gauntlet rooms 1-3, golden file suite, and client QA harness — so every future sprint can be validated end-to-end.

docs/sprints/sprint-9/joint.md

@@ -1,3 +1,12 @@
+---
+title: "Sprint 9 — Joint Briefing"
+description: "Test infrastructure backbone, Gauntlet rooms, golden file suite, client QA harness"
+type: sprint
+status: archived
+sprint: 9
+team: "joint"
+---
+
 # Sprint 9: Gauntlet — Joint / Integration
 
 **Goal:** Build the test infrastructure backbone — test client binary, Gauntlet rooms 1-3, golden file suite, and client QA harness — so every future sprint can be validated end-to-end.

docs/sprints/sprint-9/server.md

@@ -1,3 +1,12 @@
+---
+title: "Sprint 9 — Server Briefing"
+description: "Test client binary, Gauntlet rooms 1-3, golden file suite, subprocess tests"
+type: sprint
+status: archived
+sprint: 9
+team: "server"
+---
+
 # Sprint 9: Gauntlet — Server Tasks
 
 **Goal:** Build the test infrastructure backbone — test client binary, Gauntlet rooms 1-3, golden file suite, and client QA harness — so every future sprint can be validated end-to-end.