Bump VERSION to 0.2.8, finalize changelog

Team admin settings audit (pass 1): remove dead BYOK/provider/persona
vestiges from team store, models, policy defaults, workflow stage UI,
and ICD tests. Fix stale chat_only stage mode in frontend to match
backend CHECK constraint.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/store/postgres/helpers.go

@@ -19,8 +19,7 @@ func SetDB(db *sql.DB) {
 }
 
 // ── Dynamic SQL Builder ─────────────────────
-// Replaces the copy-pasted addClause/addField pattern
-// found in admin.go, personas.go, team_providers.go, apiconfigs.go.
+// Replaces the copy-pasted addClause/addField pattern.
 
 // UpdateBuilder constructs a dynamic UPDATE statement.
 type UpdateBuilder struct {