fix: refuse invalid quality-loop round budgets

[HomenShum]

An agent invoking iterate.mjs could receive exit0 without any judgment for zero, negative or nonnumeric round budgets, or after a failed judgment with a fractional budget. Validate a positive safe integer before work starts, reject explicit empty/missing values, and preserve the omitted one-round default. Update the guided documentation and affected tour citations.

Validation: independent source/simplification review approved the five-file change. Independent runtime replay passed15/15 frozen scenarios; substituting only the original iterator failed all9 admission cases while6 control scenarios still passed. A separate paired1.5 case reproduced original failed judgment followed by exit0; the patch refused it before any child call. Controls cover exact exhaustion, recovery, absent-verdict failure, four separate concurrent jobs and twelve sequential history appends.

Local and Linux CI passed44 tests,49 syntax checks,36 tour/34 prose citations and the committed evidence proof. CI also passed the existing bundled smoke render (286,290 bytes); its checkout tree matches the reviewed commit. Synthetic judgments prove iterator control, not rubric/provider quality, production, same-output concurrent writes or practical large-budget endurance. No dependency, lock, workflow, model or visual changes.