Add Live Tennis app

Author: Ben

apps/livetennisscores/README.md

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+# Live Tennis
+
+Live **point-by-point** tennis scores on your Tidbyt, across the ATP, WTA,
+Challenger and ITF tours.
+
+![Live Tennis](live_tennis_scores.gif)
+
+Each live match gets its own page and the app rotates through them:
+
+```
++----------------------------------+
+| Toronto                       QF |  <- tournament + round (bg colour = tour)
+|   Alcaraz                1  2 40 |  <- sets won / games this set / current point
+| * Sinner                 1  1 AD |  <- green dot = this player is serving
+| 6-3 4-6                     LIVE |  <- completed sets            live/tiebreak
++----------------------------------+
+```
+
+* **Sets won** in white, **games in the current set** in blue, **current point**
+  (`0 / 15 / 30 / 40 / AD`) in yellow.
+* During a tiebreak the point column turns orange and the status reads `TB`.
+* The header background identifies the tour: blue = ATP, magenta = WTA,
+  brown = Challenger, grey = ITF.
+* A player slot that has not been filled yet (qualifier / lucky loser) shows
+  `TBD`, and a match with no score yet shows `About to start`.
+
+## Setup
+
+1. Get a **free** Live Tennis API key (1,000 requests/day) at
+   <https://livetennisapi.com/subscribe/free>.
+2. Paste it into the app's **API key** field in the Tidbyt mobile app.
+3. Optionally pick a single tour, set the rotation speed, and turn on rankings.
+
+## Requests
+
+The app fetches `GET /matches?status=live` with `ttl_seconds = 120`, so one
+key/tour combination makes at most `86400 / 120 = 720` upstream requests a day —
+inside the 1,000/day free tier.