docs: document guard_exclude_paths, trim its config comment, fix max_rounds default

[TON14]

guard_exclude_paths landed in #28, but neither README mentions it, so the only description of the setting is the comment in the generated config — and that comment now runs six lines, five of which restate validation rules an operator cannot act on while editing the file.

Rebased onto 0.1.7.

Trim the config template comment

CONFIG_TEMPLATE keeps the part that helps at the point of edit — what the key is for, a concrete example, that agents still read excluded paths, and the replace semantics added in #56 — matching the one-to-three-line comments on the surrounding keys. The validation rules move to the README.

Document the setting in both READMEs

A [run] table row plus a paragraph under the table, in README.md and README.zh-CN.md, covering what the comment no longer says:

• every exclusion is a hole in the audit, since the guard is the only witness of workspace mutations and the agents keep Bash access to the excluded path;
• exclusions resolve against the workspace and must stay inside it, and .git and harness-owned control/state paths are rejected at startup, with the run refusing to start on the first violation;
• the effective list is echoed at run start and recorded per audited episode as verifier_guard_exclude_paths;
• --guard-exclude-path is repeatable and replaces the configured list rather than adding to it, per _apply_repeatable_defaults.

Correct the documented max_rounds default

Both READMEs advertise 30 in the [run] table and in the CLI options list, while DEFAULT_MAX_ROUNDS, the config template, and lh-harness run --help all say 25.

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Documentation only — no behavior change. pytest: 404 passed, 2 skipped.