Issue #3614378: Repair the wording the mechanical rename damaged, in English and in French

Follow-up to !129 (merged), same issue. The mechanical rename damaged wording that a blanket replacement cannot get right, and all of it is user-facing.

English

A category groups one or more grades became A tariff classes one or more grades, because "groups" was a verb there. It reads "groups" again. Also across price tariffs in the placement module's description (redundant) and the bookable price tariffs for the slot in a docblock.

French, gender

Catégorie is feminine, tarif is masculine, so 14 strings kept the wrong article, demonstrative or participle: "Ajouter une tarif", "cette tarif", "de la tarif", "les nouvelles tarifs", "proposée", "sélectionnée", "Lorsqu'elle est activée … désactivez-la".

French, sense

Worse than agreement: the pass renamed catégorie where it meant a seat grade, which is the conflation this rename exists to remove. "Pool grade" read Tarif de la jauge, "Grades of its places" read Tarifs de ses places, and the pool-grade description opened La tarif de place au tarif de laquelle, which means nothing. Those say grade now, along with the declared-grade validation messages.

Verification

The catalogue was imported into a running site and the rendered strings read back (Ajouter un tarif, Grade de la jauge, Grades de ses places, dans le même tarif). Both directions checked: all 42 entries mentioning tariff or quota exist in source, msgfmt -c validates 1206 messages, and the five affected kernel suites pass.