feat: add documents duplicate command for template instantiation (#40)

[teslakoile]

Summary

Adds a new huly documents duplicate DOC_ID --title "..." subcommand that compresses the 4-5 step template-instantiation workflow (describe → save → create → set-file → re-parent) into a single command. Inherits the source's space and parent by default; --space or --parent override either.

Changes

• src/huly_cli/commands/documents.py

  • Adds the duplicate Typer command. Internally composes existing CRUD: _find_document_by_id (source + re-fetch), _resolve_teamspace_by_name (only when --space is passed — branches cleanly to avoid resolving the already-ID source space), client.tx for the create, then the same create-content + update-tx path describe --set-file uses.
  • Extracts two small private helpers — _read_doc_markdown(client, doc) and _write_markdown_to_doc(client, auth, doc, md) — so both describe and duplicate share the inline-vs-blob read path and the create-content write path. describe --set now delegates to _write_markdown_to_doc.
  • No changes to client.py, markup.py, or output.py.

• tests/test_issue_write_path.py

  • Seven CliRunner command-layer tests covering: inherited space+parent, --space override (teamspace name resolution), --parent override, --json full-record return, source-not-found error, missing --title (required option), and that the content copy path uses create_content (not set_content) against a brand-new empty doc.
  • Adds a narrow autouse fixture to reset the module-level JSON-mode flag between tests in this file (previously leaked from earlier --json tests).

• README.md — adds documents duplicate to the example command block plus a one-paragraph note on inheritance behavior.

• skills/huly-cli/SKILL.md — lists duplicate in the documents command surface and adds a short "clone the weekly template" agent workflow example.

Test plan

• uv run pytest -x — 273 tests pass (7 new)
• uv run ruff format . && uv run ruff check . — clean
• Scope verified via git diff master --stat — only the four allowed files touched; no changes to client.py, markup.py, output.py, or unrelated command modules.
• Behavior covered: default inheritance, both overrides, --json, not-found, missing-title, and that new-doc content is written through create_content (not set_content).

Closes #40