docs: fix env init template to avoid parser-first guidance

[willccbb]

Motivation

• Reduce parser-centric guidance surfaced to authors when scaffolding new environments so docs focus on task/rubric behavior rather than parser internals.
• Ensure the prime env init README template matches the prior cleanup of per-environment README.md files and does not encourage using Parser objects by default.

Description

• Rewrote the environment README templates under environments/*/README.md to remove explicit - **Parser**: metadata lines and to reword parser-heavy phrasing in example summaries (various environment READMEs updated).
• Updated the generator template in verifiers/scripts/init.py to replace the - **Parser**: line with a neutral - **Output format expectations (optional)**: line so newly-created READMEs no longer prompt parser-first documentation.
• Minor whitespace/format fixes applied to several README.md files as part of the cleanup.

Testing

• Searched repository README templates with ripgrep to confirm the **Parser** template line was removed from verifiers/scripts/init.py using rg (search for parser-related phrases). The search showed the new Output format expectations line present and no **Parser** template line in the init template.
• Ran a local smoke test by calling init_environment('demo-env', path=<tmpdir>) from verifiers.scripts.init and inspected the generated README.md to verify it does not contain **Parser** and does contain **Output format expectations (optional)** (test succeeded).
• Verified the file change applied cleanly with a local commit and the follow-up PR metadata was created.

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Codex Task

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Note

Low Risk
Docs-only/template changes with no runtime behavior impact beyond the text generated by prime env init.

Overview
Updates the environment documentation to remove parser-centric guidance: per-environment README.md files and the top-level environments/README.md drop explicit **Parser** metadata lines and reword a few descriptions to focus on task/rubric behavior instead of parser internals.

Adjusts prime env init’s README_TEMPLATE (verifiers/scripts/init.py) to replace the **Parser** placeholder with a neutral **Output format expectations (optional)** line, and applies minor Markdown/whitespace fixes (including newline-at-EOF cleanup).

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