v0.19.0 - MCP Write Tools Return Frontmatter-Only

Changed

• On a successful write, the generic update, set_status (its twelve
  non-adr adapters), and set_classification tools, and every
  per-domain create_<d> tool (req/uc/tsk/qa/prb/gol/rsk/
  dec/sop/feat/vcr/sysrs), now return the domain's frontmatter
  object only, instead of the full document with its (potentially large,
  ever-growing) body. The adr dispatch branch of set_status and every
  ADR-specific tool (create_adr, update_frontmatter, update_section,
  the option_* tools) are unchanged and still return the full document
  (GitHub issue #69).