diplomail (Stage A): add in-game personal mail subsystem

Phase 28 of ui/PLAN.md needs a persistent player-to-player mail
channel; the existing `mail` package is a transactional email
outbox and the `notification` catalog is one-way platform events.
Stage A lands the schema (diplomail_messages / _recipients /
_translations), a single-recipient personal send/read/delete
service path, a `diplomail.message.received` push kind plumbed
through the notification pipeline, and an unread-counts endpoint
that drives the lobby badge. Admin / system mail, lifecycle hooks,
paid-tier broadcast, multi-game broadcast, bulk purge and language
detection / translation cache come in stages B–D.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/internal/postgres/jet/backend/table/diplomail_translations.go

@@ -0,0 +1,96 @@
+//
+// Code generated by go-jet DO NOT EDIT.
+//
+// WARNING: Changes to this file may cause incorrect behavior
+// and will be lost if the code is regenerated
+//
+
+package table
+
+import (
+	"github.com/go-jet/jet/v2/postgres"
+)
+
+var DiplomailTranslations = newDiplomailTranslationsTable("backend", "diplomail_translations", "")
+
+type diplomailTranslationsTable struct {
+	postgres.Table
+
+	// Columns
+	TranslationID     postgres.ColumnString
+	MessageID         postgres.ColumnString
+	TargetLang        postgres.ColumnString
+	TranslatedSubject postgres.ColumnString
+	TranslatedBody    postgres.ColumnString
+	Translator        postgres.ColumnString
+	TranslatedAt      postgres.ColumnTimestampz
+
+	AllColumns     postgres.ColumnList
+	MutableColumns postgres.ColumnList
+	DefaultColumns postgres.ColumnList
+}
+
+type DiplomailTranslationsTable struct {
+	diplomailTranslationsTable
+
+	EXCLUDED diplomailTranslationsTable
+}
+
+// AS creates new DiplomailTranslationsTable with assigned alias
+func (a DiplomailTranslationsTable) AS(alias string) *DiplomailTranslationsTable {
+	return newDiplomailTranslationsTable(a.SchemaName(), a.TableName(), alias)
+}
+
+// Schema creates new DiplomailTranslationsTable with assigned schema name
+func (a DiplomailTranslationsTable) FromSchema(schemaName string) *DiplomailTranslationsTable {
+	return newDiplomailTranslationsTable(schemaName, a.TableName(), a.Alias())
+}
+
+// WithPrefix creates new DiplomailTranslationsTable with assigned table prefix
+func (a DiplomailTranslationsTable) WithPrefix(prefix string) *DiplomailTranslationsTable {
+	return newDiplomailTranslationsTable(a.SchemaName(), prefix+a.TableName(), a.TableName())
+}
+
+// WithSuffix creates new DiplomailTranslationsTable with assigned table suffix
+func (a DiplomailTranslationsTable) WithSuffix(suffix string) *DiplomailTranslationsTable {
+	return newDiplomailTranslationsTable(a.SchemaName(), a.TableName()+suffix, a.TableName())
+}
+
+func newDiplomailTranslationsTable(schemaName, tableName, alias string) *DiplomailTranslationsTable {
+	return &DiplomailTranslationsTable{
+		diplomailTranslationsTable: newDiplomailTranslationsTableImpl(schemaName, tableName, alias),
+		EXCLUDED:                   newDiplomailTranslationsTableImpl("", "excluded", ""),
+	}
+}
+
+func newDiplomailTranslationsTableImpl(schemaName, tableName, alias string) diplomailTranslationsTable {
+	var (
+		TranslationIDColumn     = postgres.StringColumn("translation_id")
+		MessageIDColumn         = postgres.StringColumn("message_id")
+		TargetLangColumn        = postgres.StringColumn("target_lang")
+		TranslatedSubjectColumn = postgres.StringColumn("translated_subject")
+		TranslatedBodyColumn    = postgres.StringColumn("translated_body")
+		TranslatorColumn        = postgres.StringColumn("translator")
+		TranslatedAtColumn      = postgres.TimestampzColumn("translated_at")
+		allColumns              = postgres.ColumnList{TranslationIDColumn, MessageIDColumn, TargetLangColumn, TranslatedSubjectColumn, TranslatedBodyColumn, TranslatorColumn, TranslatedAtColumn}
+		mutableColumns          = postgres.ColumnList{MessageIDColumn, TargetLangColumn, TranslatedSubjectColumn, TranslatedBodyColumn, TranslatorColumn, TranslatedAtColumn}
+		defaultColumns          = postgres.ColumnList{TranslatedSubjectColumn, TranslatedAtColumn}
+	)
+
+	return diplomailTranslationsTable{
+		Table: postgres.NewTable(schemaName, tableName, alias, allColumns...),
+
+		//Columns
+		TranslationID:     TranslationIDColumn,
+		MessageID:         MessageIDColumn,
+		TargetLang:        TargetLangColumn,
+		TranslatedSubject: TranslatedSubjectColumn,
+		TranslatedBody:    TranslatedBodyColumn,
+		Translator:        TranslatorColumn,
+		TranslatedAt:      TranslatedAtColumn,
+
+		AllColumns:     allColumns,
+		MutableColumns: mutableColumns,
+		DefaultColumns: defaultColumns,
+	}
+}