Synthetic typo corpora, published error budgets, and suggestion reporting

1. The synthetic corpora are verifiable by construction: every correction is a dictionary stem, every misspelling is reachable by a declared keyboard-noise operation, and the whole file is a seeded pure function of the dictionary pin. The headline measurement is that even the full tier can embed only about 1.5% of these realistic misspellings, which quantifies the gap between embedding tiers and actual misspellings and motivates the dictionary sweep.
2. The performance documentation now carries the tier error budget, listing worst-case rank correlation and top-1 agreement across all 55 languages next to the gates that enforce them, so every claim about a cheaper tier carries its measured number.
3. The playground popover gained a report link: one click opens a pre-filled issue with the word, the offered suggestions, the language, and the engine version, and nothing else. Verified reports feed the corpora.
4. The Docker CI image could not install kotoshu at all once the native extension shipped; a newly added version guard caught the failure on its first run, and the image now builds the Rust accelerator properly.

see also Error budgets · Playground