move server code into server/, update docs

- app.py + upstream.py -> server/ (relative import, __init__.py)
- static/ resolved relative to repo root, works from any CWD
- watch history migrated to server/data/history.json
- README.md: quick start, features, layout, dev notes
- SPEC.md: marked implemented, updated endpoints/run/deviations
- ignore *.tar.gz (local curl-impersonate download at repo root)

run.sh

@@ -2,6 +2,6 @@
 # launch (or restart) the ani-web server
 cd "$(dirname "$0")" || exit 1
 [ -x .venv/bin/python ] || { echo "no .venv — run: uv venv .venv && uv pip install --python .venv/bin/python -r requirements.txt"; exit 1; }
-pkill -f "[u]vicorn app:app" 2>/dev/null; sleep 1
-nohup .venv/bin/python -m uvicorn app:app --host 0.0.0.0 --port 8321 > server.log 2>&1 &
+pkill -f "uvicorn .*app:app" 2>/dev/null; sleep 1
+nohup .venv/bin/python -m uvicorn server.app:app --host 0.0.0.0 --port 8321 > server.log 2>&1 &
 echo "ani-web on http://localhost:8321 (pid $!)"