Every setting of discriminator and rproxy is read through viper, in place
of the os.LookupEnv function Main passed down. NewViper turns AutomaticEnv
and AllowEmptyEnv on, so a setting that is set but empty reads as set. A
setting may also be given as a file, the _FILE form, which rproxy's
settings now have too; rproxy still writes nothing to disk.
The settings are renamed. Discriminator's take the prefix SWW_WAF_,
rproxy's take SWW_RPROXY_, and the shared SWW_COMMAND keeps SWW_. The Core
Rule Set's settings take SWW_WAF_CORE_RULE_SET_ rather than SWW_WAF_WAF_.
Model: deepseek-v4-pro (first version); opus-5-5 (rework)
Each discriminator check is now a type in its own file behind one small interface, listed in `heuristics.go`. Adding a heuristic is one file and one line. Behaviour does not change.
Refusal and ban log lines gain `heuristic` and `heuristic_figures`. A ban after the answer, by `refusal_limit` or `byte_limits`, logs `after_answer_heuristic` and its figures, so one line can name both.
Deviation: four lists, not the planned three, so `refusal_limit` still bans at the decision.
Rule suppressed: `//nolint:lll` on one struct tag.
Model: opus-5-5