feat(cartridge): scaffolder for boj-server cartridge skeletons (standards#89 Phase 2b) (#24)

Adds `iseriser cartridge --manifest <toml> --output <dir>` which emits a
complete boj-server cartridge skeleton at `<output>/<iser>-mcp/`:

  <iser>-mcp/
  ├── README.adoc                            cartridge overview + build
  ├── cartridge.json                         registration manifest
  ├── mod.js                                 JS-worker fallback path
  ├── panels/manifest.json                   observability panel registration
  ├── abi/
  │   ├── README.adoc
  │   ├── <iser>-mcp.ipkg                    Idris2 package
  │   └── <Iser>Mcp/Safe<Iser>.idr           exposure-gate contract + tools
  ├── ffi/
  │   ├── README.adoc
  │   ├── build.zig                          shared-shim wiring
  │   └── <iser>_ffi.zig                     ADR-0006 5-symbol C-ABI
  └── adapter/
      ├── README.adoc
      ├── build.zig
      └── <iser>_adapter.zig                 unified gated adapter (4-protocol)

The cartridge is meant to be placed inside `boj-server/cartridges/`; the
emitted Zig build files reference the shared invoke-shim at
`boj-server/ffi/zig/src/cartridge_shim.zig` via `../../../`.

Modelled on the k9iser-mcp pilot (boj-server#73).  Skeleton-only: the
exposure/transaction gate, the 5-symbol ABI plumbing, and the unified
4-protocol adapter are all production-ready; per-tool dispatch bodies
are stubs ready for replacement.

Verified end-to-end against the actual boj-server tree:
- `zig build test` on emitted ffi/   → 4/4 tests pass
- `zig build test` on emitted adapter/ → 5/5 tests pass
- `idris2 --build` on emitted .ipkg → SafeChapeliser type-checks (RC=0)
- `cargo test`: 57 unit + 9 integration green (8 new tests added)
- `zig fmt --check` on all emitted .zig files: clean
- `cartridge.json` + `panels/manifest.json` parse as valid JSON

Two pilot-vs-scaffold deltas worth noting:
- The pilot `.ipkg` ships `depends = base, contrib` which is invalid in
  Idris2 0.8.0 (parser stops at the comma).  The scaffold emits
  `depends = base` to compile cleanly; `contrib` can be added on a
  separate `depends` line when actually needed.
- The pilot's per-tool bodies (k9_load_manifest, k9_generate, ...) are
  k9iser-specific.  The scaffold emits one example tool
  (`<iser>_generate`) plus a status panel; expand as the cartridge grows.

Refs hyperpolymath/standards#89, #90

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

Author: hyperpolymath