feat(assets): embedded prompt and xlsx asset fallback (U10a slice 2)

- configs package embeds agents/ + shared/ prompt assets; templates package
  embeds xlsx/ (cdo_quote.xlsx)
- template.GetAgentInstructionFile: disk-first with embedded fallback for
  instructions and writing.md (dev behavior unchanged)
- quote.CalculateAndFill: embedded xlsx fallback when the on-disk template
  walk misses (single-binary deployments)
- presence test guards the embedded asset set
- verified: vet + template/quote/bizdev/squad/arch green

templates/embed.go

@@ -7,3 +7,8 @@ import "embed"
 //
 //go:embed docs/*.md
 var DocTemplates embed.FS
+
+// XlsxAssets 内嵌运行 xlsx 资产（如 cdo_quote.xlsx）；磁盘路径存在时优先磁盘。
+//
+//go:embed xlsx
+var XlsxAssets embed.FS