feat: import 16 OSWorld LibreOffice tasks as computer-use environments

[Aling33]

Closes #24.

Adds scripts/import_osworld.py, which imports 16 OSWorld LibreOffice tasks (13 Calc + 3
Writer, within the issue's 10-20 scope) as computer-use environments, one folder per task,
following the computer_use/signup_form layout.

Each generated folder

• task.md — the task's own instruction, plus where the file is (open in Calc or Writer
  and at ~/Desktop/<file>) and to save with Ctrl+S.
• setup.sh — decodes the staged assets/<file>.b64 to the Desktop and opens it in
  LibreOffice; fails loudly if soffice/libreoffice is missing, so a missing app is a
  setup error, not a silent zero. These tasks' configs are exactly a download plus an
  open, and that is what the script runs.
• verifier.py — ports the task's own OSWorld evaluator to a state check over the saved
  file, never a screenshot:
  • Calc: the task's compare_table rules (sheet name / single cell / partial sheet
    data, OSWorld's read_cell_value semantics, pandas rounding) against the saved
    workbook;
  • Writer: exact text against the reference document.
  • Rules the untouched input already satisfies are guards, not progress checks: on
    one task a naive port paid 0.5 for changing nothing, and OSWorld's evaluator
    (all-or-nothing) can't tell a re-save from real work once a rule passes on the input.
    Guards make an untouched or deleted file score 0, while partial solutions earn the
    share of progress rules done.

Verification (offline, against OSWorld's real task configs and files)

• The ported rule engine cross-checked cell-by-cell against OSWorld's own evaluator on
  the 16 real tasks: 1967 checks, 0 mismatches (including pandas' half-to-even
  rounding).
• End-to-end through the real loader + verifier: all 16 score solved 1.0 / untouched
  0.0 / missing 0.0.
• deepgym check passes on all 16 folders.
• New tests/office_fixtures.py (stdlib-only .xlsx/.docx builders) and
  tests/test_import_osworld.py (32 tests) covering the importer, the evaluator port
  and the guards split.

Also in this PR: deepgym check on computer-use folders (the imports couldn't be
checked without it; it mirrors the skips deepgym qa makes since #68)

• The files check no longer demands a reference_solution.* no desktop env ships; a
  shipped reference_actions.json stays optional — an agent drives the desktop.
• The run checks report a skipped reference_passes when there is no episode to replay,
  or when the env needs a desktop (--mode daytona replays the built-ins' episodes),
  instead of failing over a reference a local session can't run.
• lint_env reads a computer-use verifier the way the loader prepends it (_checks.py +
  PARAMS).

License — OSWorld is Apache-2.0; the imported task configs, instructions and files
keep its license (noted in the README section on the import).

Notes

• The importer falls back to the GitHub contents API and hf-mirror.com where the usual
  raw hosts are blocked; the imported data was verified against a cached manifest.
• The issue lists LibreOffice as part of the Daytona desktop; setup.sh still checks for
  the binary explicitly.

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[Aling33]

Thanks for taking this over and for the thorough pass — the reference episodes for every task and the hardened, bounded readers make this much stronger than my original. I'll stay off the branch; happy to pick up anything if useful.