Name log fields, metrics and the Core Rule Set package for what they are (closes #192)

The first half of the naming audit: names now say what they are. `internal/waf` is `internal/coreruleset`. Log fields, the action `blocked_by_core_rule_set`, the metric and the alert event say Core Rule Set. Timings end `_ms`. Percentages say of what, as `rate_limit_percent` and `bytes_limit_percent`. Setting names follow in #234.

Judgement call: `blocked_by_core_rule_set`, not the audit's `core_rule_set_blocked`, to match `blocked_by_block_rule`.
Trips a reader: an existing state file holding `waf_blocked` or the anomaly scope `watch` stops the start and must be removed. `SWW_ALERT_EVENTS` listing `waf_block` must list `core_rule_set_match`.

Model: opus-5-5

internal/discriminator/health_test.go

@@ -21,7 +21,8 @@ func TestHealthEndpointCountsTowardNoLimit(t *testing.T) {
 	)
 
 	for range healthChecks {
-		got := s.adminRequest("", http.MethodGet, discriminator.HealthPath, "", http.StatusOK)
+		got := s.ownEndpointRequest("", http.MethodGet, discriminator.HealthPath, "",
+			http.StatusOK)
 
 		if string(got.body) != "ok\n" || got.header.Get("Content-Type") != contentType {
 			t.Errorf("health endpoint answered %q with Content-Type %q, want ok "+