Translations: missing strings show in English and are listed by a report, not failed by tests (#2244)

* Translations: delete coverage and wording tests

A missing translation shows in English and never fails a test. Delete the
coverage and per-language parity tests, the tests that pin one language's
wording and the source scans for strings not routed through the catalog.
Keep the stale-row, duplicate-row and placeholder checks, and make the
engine tests that switch language compare against the catalog instead of a
literal. Drop the Traditional Chinese panel rows that only repeated the
English source to satisfy the parity test.

* Translations: missing-strings report in xtask ci

missing_translations_report prints, per language, the fixed menu entries,
panel strings, effect names and effect categories with no row. It always
passes. cargo xtask ci runs it with --nocapture after the test runs, so the
list shows in the gate log. The docs say a missing string shows in English
and where the list is.

docs/testing.md

@@ -6,7 +6,9 @@ cargo xtask ci             # fmt, clippy -D warnings, tests, layers, assets, was
 ```
 
 `cargo xtask ci` builds in the dev profile and runs the tests with `cargo nextest run` (plus
-`cargo test --doc`) when `cargo-nextest` is installed, and with `cargo test` otherwise.
+`cargo test --doc`) when `cargo-nextest` is installed, and with `cargo test` otherwise. It then
+runs `missing_translations_report` with `--nocapture`, which prints the interface strings each
+language has no translation for. Those strings show in English; the report always passes.
 
 Each crate with several integration-test files has one test binary, `tests/it/main.rs`, whose
 modules are the files in `tests/it/`. Run one file with `cargo test -p <crate> --test it <module>::`