revert(scaffold): remove wrong-place adapter emission (standards#89 sub-issue 1) (#28)

The unified transaction-gated adapter belongs to the boj-server cartridge
(boj-server/cartridges/<name>-mcp/adapter/), not to the new -iser repo.

The pilot k9iser confirms this: k9iser has no adapter; its adapter lives
at boj-server/cartridges/k9iser-mcp/adapter/k9iser_adapter.zig.

iseriser PR#12 emitted adapter/<name>_adapter.zig into the new -iser repo
where it had no FFI module to import (`@import("<name>_ffi")` against
nothing), no build.zig, and no cartridge.json. The emitted dispatch was
a stub that discarded tool+body, only two of four advertised protocols
were routed, and a buffer-aliasing bug between dispatchRest and the HTTP
response writer would have corrupted output if any FFI were attached.

Surgical revert:
- Drop generate_unified_adapter (213 lines).
- Drop the call site and its doc-comment marker.
- Update test threshold 22 → 21 (base + regen workflow only).
- Drop the adapter-existence assertion in test_files_written_to_disk.
- Update the CI/CD generator header to document why the adapter is not
  emitted here and where it belongs (cartridge-skeleton codegen is
  tracked under standards#89 Phase 2b).

Keeps generate_regen_workflow unchanged — .github/workflows/<name>-regen.yml
correctly belongs in the -iser repo (it triggers the cartridge in boj-server).

Verification: cargo build clean; cargo test 49 unit + 9 integration green.

Refs hyperpolymath/standards#90

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath