UI: unified design system, light/dark themes, redesigned pages and player UI

Tokens and components in styles.css, shared Ui (dialogs, toasts), icons,
bottom tab bar on mobile, keyboard/gamepad navigation, library shelf with
filters and conversion badges, hero game page, restyled player screens.
Games list now returns per-game version counts. Adds docs/UI_DESIGN.md.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

backend/app/models.py

@@ -57,6 +57,9 @@ class Game(Base):
     tags: Mapped[list[str]] = mapped_column(ARRAY(String), default=list)
     engine: Mapped[str] = mapped_column(String(32), default="renpy")
     cover_hash: Mapped[str | None] = mapped_column(String(80))
+    # the version "Play" opens; translations are published by merging into it
+    main_version_id: Mapped[int | None] = mapped_column(
+        ForeignKey("game_versions.id", ondelete="SET NULL", use_alter=True))
     created_by_id: Mapped[int | None] = mapped_column(ForeignKey("users.id", ondelete="SET NULL"))
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
 
@@ -74,6 +77,9 @@ class GameVersion(Base):
     description: Mapped[str] = mapped_column(Text, default="")
     # uploading -> queued -> converting -> ready | failed; importing = app.import_dir run
     status: Mapped[str] = mapped_column(String(16), default="uploading", index=True)
+    # draft: visible to the owner and reviewers only
+    visibility: Mapped[str] = mapped_column(String(16), default="published")
+    kind: Mapped[str] = mapped_column(String(16), default="original")  # original|translation|mod
     progress: Mapped[str] = mapped_column(String(255), default="")
     upload_name: Mapped[str | None] = mapped_column(String(255))
     manifest: Mapped[dict[str, Any] | None] = mapped_column(JSONB)
@@ -84,6 +90,19 @@ class GameVersion(Base):
     owner: Mapped[User | None] = relationship(lazy="joined")
 
 
+class VersionHistory(Base):
+    """Previous manifests of a version that was changed in place (e.g. a merged translation)."""
+    __tablename__ = "version_history"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    version_id: Mapped[int] = mapped_column(ForeignKey("game_versions.id", ondelete="CASCADE"),
+                                            index=True)
+    user_id: Mapped[int | None] = mapped_column(ForeignKey("users.id", ondelete="SET NULL"))
+    note: Mapped[str] = mapped_column(String(255), default="")
+    manifest: Mapped[dict[str, Any]] = mapped_column(JSONB)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+
+
 class Save(Base):
     __tablename__ = "saves"
     __table_args__ = (UniqueConstraint("user_id", "version_id", "slot"),)