Game Widget POC

Lands the Nova-only Games widget infrastructure without any actual games
registered, as the first patch in a stack that will add games one per
follow-up commit.

What ships in this shell:

• Widget registry entry (id "games") with validSizes: ["large"], plus
  PREF_WIDGETS_GAMES_ENABLED, PREF_GAMES_SIZE, and
  PREF_WIDGETS_SYSTEM_GAMES_ENABLED. resolveWidgetSize() now respects
  validSizes for all widgets.
• PREFS_CONFIG entries for widgets.games.{enabled,size,interaction,
  highScores,popoutOnly} and widgets.system.games.enabled, plus matching
  AboutPreferences wiring.
• Games widget container (Games.jsx) with game selection, popout
  (window.name "games-popout"), context menu, high-score map, and
  celebration. With an empty GAME_REGISTRY it renders the welcome state.
• GameEndOverlay shared component for per-game use later.
• GamesSizePromptToast: shown when the user tries to shrink Games
  below its valid sizes; offers a pop-out action. Animation duration
  bumped to 12s so the user can read and act.
• Customize menu Games toggle (Nova WidgetsManagementPanel) gated on
  mayHaveGamesWidget, with a WIDGET_GAMES telemetry event source.
• Nimbus + trainhop wiring in Base.jsx (mayHaveGamesWidget,
  enabledWidgets.gamesEnabled), propagated through CustomizeMenu and
  ContentSection.
• newtab.ftl: shell + generic gameplay strings only. preferences.ftl:
  home-prefs-games-header.
• Tests: WidgetsRegistry order, Widgets render-and-toggle, and
  WidgetsManagementPanel toggle behaviour extended for "games".

Out of scope (follow-up commits, one per game): the 10 game modules
under Games/titles/, the per-game l10n strings, the mozmatch asset
folder, and the per-game SCSS @imports.

Adds the first game to the Games widget: MozTacToe, a 3x3 tic-tac-toe
against a CPU opponent. No high score.

• Adds Games/titles/MozTacToe/ with the React component, SCSS, and
  game-logic module.
• Registers it in Games/titles/index.mjs (first GAME_REGISTRY entry).
• Re-introduces the per-game SCSS @import in _Games.scss.
• Adds per-game l10n strings (game label + win/loss/draw).

Parent: Bug 2039394 Games widget shell.

Adds the second game to the Games widget: Mozong, a small Pong-style
game played against a CPU opponent. First to 5 points wins. No
persistent high score.

• Adds Games/titles/Mozong/ with the React component, SCSS, and
  game-logic module.
• Registers it in Games/titles/index.mjs.
• Adds the per-game SCSS @import in _Games.scss.
• Adds per-game l10n strings (game label, canvas aria-label, win/loss).

Parent: Bug 2039394 Add MozTacToe game.

Adds the third game to the Games widget: MozFour, a Connect Four-style
game played against a CPU opponent on a 7x6 board. No persistent high
score.

• Adds Games/titles/MozFour/ with the React component, SCSS, and
  game-logic module.
• Registers it in Games/titles/index.mjs.
• Adds the per-game SCSS @import in _Games.scss.
• Adds per-game l10n strings (game label, win/loss/draw).

Parent: Bug 2039394 Add Mozong game.

Adds the fourth game to the Games widget: MozBattle, a Battleship-style
fog-of-war game against a CPU opponent. 7x7 board with three small
ships (1x3, 1x2, 1x2). Player only sees their shots on the CPU grid;
remaining ship counts are shown for both sides above the board. No
persistent high score.

• Adds Games/titles/MozBattle/ with the React component, SCSS, and
  game-logic module (auto-placement, pure shot reducers, hunt-and-
  target CPU AI).
• Registers it in Games/titles/index.mjs.
• Adds the per-game SCSS @import in _Games.scss and includes the
  game in the shared position-relative selector list.
• Adds per-game l10n strings (game label, fleet labels, status
  messages for player/CPU miss/hit/sunk, win/loss).

Parent: Bug 2039394 Add MozFour game.

Lays the foundation for card-based games in the Games widget (War,
Blackjack, Poker). No new game is added in this commit; this is pure
scaffolding.

• Adds Games/deck.mjs with createDeck/shuffle/deal helpers and shared
  suit/rank constants. Random is injectable for deterministic tests.
• Adds Games/Card.jsx — a small renderer for a single playing card,
  with face-up and face-down (diagonal-hatch back) variants.
• Adds Games/_cards.scss — shared card visual treatment used by all
  card-based games (border, shadow, corner labels, big center pip,
  red/black colors based on suit).
• Adds GameRegistryEntry.hasDifficulty (typedef in titles/types.mjs)
  so games whose CPU makes no decisions (e.g. War) can suppress the
  Difficulty submenu.
• Wires Games.jsx to gate the Difficulty submenu by activeGame's
  hasDifficulty (default true preserves existing behavior).
• Adds the Card.jsx karma coverage override matching the pattern used
  by other Games .jsx files.

Parent: Bug 2039394 Add MozBattle game.

Adds the fifth game to the Games widget: MozWar, a classic two-player
card game where higher rank wins both cards, with the "war" tie-break
when both players draw the same rank. No CPU strategy — outcomes are
fully determined by the shuffled deck — so the widget's Difficulty
submenu is hidden while MozWar is active.

• Adds Games/titles/MozWar/ with the React component, SCSS, and pure
  game-logic module (createInitialState, playRound, getStatusId).
• War declaration is a separate click: ties pause in a "warPending"
  phase and show "WAR!" before the player clicks "Declare war" to
  resolve the 3-face-down + 1-face-up tribute.
• Registers MozWar with hasDifficulty: false in titles/index.mjs.
• Adds the per-game SCSS @import in _Games.scss.
• Adds per-game l10n strings (game label, status messages, button
  labels for the war-declared state).
• Adds MozWar.test.jsx covering createInitialState, playRound for
  both idle and warPending phases (including war chains and
  insufficient-cards edge cases), wasWar, and getStatusId.
• Adds the MozWar.jsx karma coverage override matching the pattern
  used by other Games .jsx files.

Parent: Bug 2039394 Add card-game shared infrastructure.