mutation.adoc documents UPSERT the generator refuses at dispatch

docs/manual/reference/directives/mutation.adoc still teaches @mutation(typeName: UPSERT) as a working verb: it appears as a documented enum value with ON CONFLICT semantics and row-identification prose (about nine mentions on the page). The generator refuses the verb at classifier dispatch with "not yet supported; the conflict-target’s uniqueness and the bulk-UPSERT cardinality story are not designed" (FieldBuilder’s DML-kind dispatch), the example schema carries no upsert field, and the `directives.graphqls doc-comment already states the refusal. A reader following the manual authors a schema the build rejects.

Surfaced during the R519 docs sweep, which removed only UPSERT’s @table-on-input dependencies and left the broader staleness in place as out of scope for that item.

Fix shape: cut the page’s UPSERT sections down to the same one-line refused-for-now statement the SDL doc-comment makes (keeping the enum value listed, since the declaration still declares it), or, if UPSERT support is genuinely near, leave the prose and say so explicitly with a "not yet implemented" banner. Either way the page must stop describing unimplemented ON CONFLICT behavior as current. Check deprecations.adoc and the tutorial for echoes while in there.