feat: add documents discovery filters and title resolvers (#37)

[teslakoile]

Summary

Adds discovery filters and title-based resolvers to the documents command group so agents don't have to list → --json → jq → copy ID → get/describe. All three additions are client-side over the existing find-all Document query — no new RPCs.

Changes

• documents list --title-contains TEXT — case-insensitive substring match on title, applied client-side after find-all. Help text notes callers should bump -n in large workspaces since the filter runs over the fetched page, not the whole workspace.
• documents list --parent DOC_ID — forwards parent into the find-all query so callers can walk a hierarchy without fetching the whole workspace.
• documents get --title TITLE and documents describe --title TITLE — case-insensitive exact title → ID resolver. If multiple documents share the title, exits 1 with a formatted (title, id) table rather than silently picking one. Argument DOC_ID is now optional; exactly one of {DOC_ID, --title} must be provided.
• documents search "query" — new command; currently a client-side title-substring filter (thin wrapper over --title-contains). Will swap the backend to /search-fulltext once search: add top-level search command using confirmed-working /search-fulltext endpoint #41 lands.

Docs updated: README.md (documents usage examples) and skills/huly-cli/SKILL.md (document discovery helpers block + documents row in command groups).

Scope stayed within src/huly_cli/commands/documents.py, tests/test_commands.py, README.md, and skills/huly-cli/SKILL.md. No changes to client.py, output.py, or any other command module.

Test plan

• uv run ruff format . && uv run ruff check . — clean
• uv run pytest -x — 277 passed (266 before + 11 new command-layer tests)
• New tests cover: title-contains filter, parent filter (asserts parent forwarded into the find-all query), title resolver unique match (get + describe), title resolver multiple-match error with match table, title resolver not-found, both-args error, neither-args error, search happy path, search empty result.

Closes #37