Add docs navigation and tighten API request security

docs/gitbook/playing.md

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+# Your first game
+
+Your goal is to work out where the view was taken. You do not need to know Minecraft coordinates to enjoy a game.
+
+## Play a round
+
+1. Open [Play & maps](https://minegeo.vercel.app/servers), choose a map, and keep **Solo** selected.
+2. Pick a difficulty and click **Start exploring**.
+3. Drag the picture to look around. You can turn your view, but you cannot walk around.
+4. Look for a mountain, beach, river, road, or interesting building.
+5. Open the small map in the bottom-right corner. Click where you think you are to place a pin.
+6. Move the pin if you change your mind, then submit your guess before time runs out.
+
+## Pick your pace
+
+- **Easy:** 3 minutes per round, with zoom. A good place to start.
+- **Normal:** 90 seconds per round, with zoom.
+- **Hard:** 30 seconds per round, without zoom. Bring your detective hat.
+
+> “Just one more look around.” The timer: 0:01. 💀
+
+## How points work
+
+A closer guess earns more points. You can get up to **5,000 per round** and **25,000 across all five rounds**. If the clock runs out without a guess, that round gets zero. You can still finish the game.
+
+North is at the top of the map. Compare shapes: a bend in a river or the edge of a forest can be easier to spot than a single house.
+
+![Confused Math Lady meme: a puzzled face surrounded by equations](https://i.imgflip.com/6677gf.png)
+
+A familiar reaction when every mountain looks like your mountain. [Meme source: Imgflip](https://imgflip.com/memetemplate/373211007/Confusion).
+
+## See how you did
+
+At the end, compare your guesses with the real locations. Visit the [Leaderboard](https://minegeo.vercel.app/leaderboard) to search for players or choose a difficulty. Your best full-game score is used for ranking. Multiplayer has its own results, and private imported maps do not add leaderboard scores.