docs(rfc): refresh @org default-templates RFC to match shipped state

The RFC was last touched at "Round 4" before implementation; several
decisions emerged during landing that the document didn't reflect.
Update it to describe the design as shipped on PR #1398.

- Status header — "Implemented" + pointer to the Implementation State
  table.
- Manifest schema — drop the unshipped `keywords` field; add the
  reserved `__vp_` name-prefix note.
- Resolution Flow — point at the actual files (`org-manifest.ts`,
  `org-tarball.ts`); document `.npmrc` registry/auth retry, version
  pinning via `dist-tags` then `versions`, and the
  `<host>/<scope>/create/<version>` cache layout with sanitized host.
- Bundled-templates section — same cache-layout update.
- Implementation Plan — replace forward-looking phases with an
  Implementation State table mapping shipped concerns to concrete
  modules (org-* under create/, npm-config.ts, migrator helpers,
  utils/.gitignore guarantee, etc.).
- Testing — describe the actual snap-test fixtures under
  packages/cli/snap-tests/ (incl. the new bundled-monorepo case)
  and the unit-test surface that landed.
- Resolved Decisions — append every decision that emerged from
  review: colon separator, createConfig namespace, version pinning,
  .npmrc auth retry, __vp_ reservation, cache host segment + Windows
  sanitization, atomic extract + stale-staging cleanup, mode
  preservation, dropped keywords, gated defaultTemplate injection,
  unified git-init, .gitignore guarantee, and findWorkspaceRoot
  staying monorepo-only.

Author: fengmk2