docwriter: skill + agent migrated; commands.doc_build slot added

Third skill via the boss pattern. docwriter was the most
language-coupled of the seven (Rust rustdoc, cargo doc, /// + //!,
intra-doc links). Generalised the discipline while keeping Rust
as the canonical concrete example, with a note that other
languages substitute syntax (TSDoc, Python docstrings, Javadoc).

Profile gains one slot:
- `commands.doc_build` — doc-build command that prints warnings
  on stderr (e.g. "cargo doc --no-deps 2>&1"); used by the
  docwriter agent's verification triple and warning enumeration.
  Optional — projects without API docs omit it.

Vocabulary substitutions:
- AILang → "this project"
- "crates" → "components / packages / crates / modules" (the
  project's idiom)
- "milestone" → "cycle"
- "Boss" → "orchestrator"
- "ailang-docwriter" → "docwriter"

AILang-specific bits replaced:
- `cargo doc --no-deps 2>&1` → `commands.doc_build` slot
- `cargo build --workspace` / `cargo test --workspace` →
  `commands.build` / `commands.test` slots
- `crate / module / item` levels → "top-level / module-level /
  item-level" (the universal taxonomy; concrete syntax via
  language note)
- `src/lib.rs` / `src/main.rs` hardcoded paths → "entry-point
  file" (Rust example kept inline)
- `docs/` / `design/` hardcoded dirs → `paths.design_ledger`,
  `paths.design_contracts`, `paths.design_models`,
  `paths.spec_dir` slots

Universal substance preserved verbatim:
- Iron Law (4 lines)
- Documentation rules (5 bullets) — substantive content; only
  the concrete-syntax examples got the Rust-as-example note
- Hard limits (4 bullets)
- Verification triple (build / test / doc_build)
- Status protocol (DONE / DONE_WITH_CONCERNS / NEEDS_CONTEXT /
  BLOCKED)
- All 7 Common Rationalisations rows (with vocabulary edits)
- All 7 Red Flags bullets

docs/profile-schema.md

@@ -45,6 +45,7 @@ take the next-higher number; deleted files retire their number.
 | `build`        | string | (required)     | Build command — exit 0 means success. |
 | `test`         | string | (required)     | Test command — exit 0 means success. |
 | `lint`         | string | (optional)     | Lint command — exit 0 means success. |
+| `doc_build`    | string | (optional)     | Documentation-build command used by the `docwriter` skill. Should print warnings on stderr so the agent can enumerate them (e.g. `cargo doc --no-deps 2>&1`). Omit if the project has no API docs. |
 | `regression`   | list   | `[]`           | Regression scripts run by the audit skill. Each entry is a shell command; non-zero exit is a regress. |
 
 ## `vocabulary`