Add MTGA Assistant: native Linux deck and game tracker

PySide6 app that follows MTG Arena's Player.log under Steam/Proton and shows
my remaining library with draw odds, my zones, and everything revealed about
the opponent (board, graveyard, exile, known hand/library, seen this match).

- Auto-detects the Steam library, Proton prefix log and MTGA install
- Card names/costs/types from MTGA's local SQLite card database
- Tracks card identity across zone changes, shuffles and Bo3 games
- Scryfall card images with a lazy, size-capped LRU disk cache
- Live log following with restart detection, plus --replay mode
- Flags log gaps where MTGA omits oversized game-state messages

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

README.md

@@ -1,2 +1,64 @@
 # mtga-assistant
 
+A native Linux deck and game tracker for **Magic: The Gathering Arena** running under Steam/Proton.
+It follows MTGA's `Player.log`, much like Untapped.gg and other trackers do, and shows:
+
+- **My deck**: remaining library with draw odds, hand, battlefield, graveyard, exile, sideboard.
+  Between matches, it shows the last deck you submitted.
+- **Opponent**: battlefield, stack, graveyard, exile, cards *known* to be in their hand or library
+  (cards you saw that went back into a hidden zone, or were revealed), and every card seen this match.
+- **Card preview**: hover a card to see its image from [Scryfall](https://scryfall.com).
+
+Card names, mana costs and types come from MTGA's own local card database, so they work offline.
+
+## Requirements
+
+- MTGA installed through Steam (Proton). The log, install and card DB are auto-detected from your
+  Steam library folders.
+- **Detailed logs enabled** in MTGA: *Options → Account → Detailed Logs (Plugin Support)*.
+- [uv](https://docs.astral.sh/uv/) (`pacman -S uv`).
+
+## Running
+
+```sh
+uv run mtga-assistant                       # follow the live Player.log
+uv run mtga-assistant --replay path/to/Player-prev.log --rate 40   # replay a saved log
+uv run pytest                               # tests
+```
+
+Start it before or after MTGA: on startup it reads the existing log to catch up on a match in
+progress, then follows new lines. When MTGA restarts and replaces the log, the tracker resets.
+
+On Wayland the window's app id is `mtga-assistant`. For example, to keep it floating on another
+workspace in Hyprland:
+
+```
+windowrule = float, class:^(mtga-assistant)$
+windowrule = workspace 2, class:^(mtga-assistant)$
+```
+
+## Configuration
+
+Optional: `~/.config/mtga-assistant/config.toml`
+
+```toml
+log_path = "/path/to/Player.log"   # override auto-detection
+mtga_dir = "/path/to/steamapps/common/MTGA"
+cache_max_mb = 500                 # image cache cap
+```
+
+## Image cache
+
+Images are downloaded only for cards that actually appear, at Scryfall's `normal` size (about
+60–100 KB each), and stored in `~/.cache/mtga-assistant/images`. When the cache passes
+`cache_max_mb`, the least recently viewed images are deleted. *Cache → Clear image cache* empties it.
+
+## Known limitations
+
+- MTGA leaves oversized game-state messages out of the log ("Message summarized because one or
+  more GameStateMessages exceeded the 50 GameObject or 50 Annotation limit"), typically during board
+  wipes. Some zones can then be stale until they next change. The app detects this and shows a
+  warning.
+- After a library shuffle, a known card's position in the opponent's library is lost. It stays listed
+  under "Library … known" until it shows up again. If it is drawn without being revealed, it may
+  stay listed.