feat: stop truncating IDs in tables and add --markdown to documents describe (#38)

[teslakoile]

Summary

Two surgical output-layer fixes. Neither touches CRUD logic.

• huly documents list, huly components list, etc. no longer render the id / parent columns with Rich's ellipsis truncation, so copying an ID out of a terminal actually works.
• huly documents describe --markdown emits plain GFM to stdout — no Rich box, no reflow — so agents can diff, grep, and round-trip content back through --set-file.

Changes

• src/huly_cli/output.py — print_list now opts columns named id / parent out of default ellipsis overflow (no_wrap=True, overflow="fold"). Rule is centralized in the helper; no per-command plumbing.
• src/huly_cli/commands/documents.py — docs_describe gains --markdown (human-only flag; JSON mode already returns markdown by default). Mutually exclusive with --raw, following the same pattern as the existing --set / --set-file check.
• tests/test_commands.py — CliRunner tests:
  • documents list renders the full 24-char ID with no …
  • parent column also shows the full ID
  • components list same
  • issues list still renders short identifiers intact after the helper change
  • documents describe --markdown produces plain GFM with no Rich box chars (╭╮╰╯┏┓┗┛━) and no panel title
  • --raw + --markdown → exit 1 with a clear error
  • default rendering still uses the Rich panel
  • JSON mode + --markdown still emits the JSON envelope
• tests/test_output.py — helper-level snapshot-ish guards on print_list so the no-truncate rule cannot silently regress.
• README.md — documents the --markdown flag and the full-ID behavior.
• skills/huly-cli/SKILL.md — agent-facing guidance that describe --markdown is the preferred read path.

Test plan

• uv run pytest -x — 277 passed
• uv run ruff format . && uv run ruff check . — clean
• Manual smoke: uv run huly documents describe --help shows --markdown
• Manual smoke: rendering a real print_list with 24-char IDs shows them in full
• Scope check: git diff master --stat touches only src/huly_cli/output.py, src/huly_cli/commands/documents.py, the two test files, README.md, and skills/huly-cli/SKILL.md

Closes #38