multi-user auth (CLI-created accounts), per-user history, test suite

- server/users.py replaces credentials.py: users.json (0600), PBKDF2,
  one-time migration of the legacy single password to user admin
  (history.json -> history/admin.json)
- accounts are CLI-managed only: python -m server.users add|rm|list
  (no self-signup on an internet-exposed app); /signup route removed,
  login page back to username + password
- per-user 30-day signed session cookie (payload carries the
  username), per-user lockout, GET /api/me, POST /account/delete
- per-user watch history: server/data/history/<user>.json; ANIWEB_DATA
  env override for the data dir
- header chip: logged-in user, logout, delete account
- tests/: throwaway-server suite (port 8399, temp data dir) — 9 HTTP
  tests + 2 Playwright browser tests (login UI, real video playback
  behind auth); runs via python tests/run.py

server/users.py

@@ -0,0 +1,116 @@
+"""users.py — multi-user accounts for ani-web (PBKDF2, single json file).
+
+CLI:  .venv/bin/python -m server.users add <username>   (password via prompt)
+      .venv/bin/python -m server.users rm <username>
+      .venv/bin/python -m server.users list
+"""
+import getpass
+import hashlib
+import json
+import os
+import re
+import secrets
+import time
+from pathlib import Path
+
+DATA = Path(os.environ.get("ANIWEB_DATA", Path(__file__).parent / "data"))
+USERS = DATA / "users.json"
+SECRET = DATA / "secret.key"
+ITER = 210_000  # OWASP 2023 minimum for PBKDF2-SHA256
+NAME_RE = re.compile(r"^[a-z0-9_-]{3,32}$")
+
+
+def get_secret() -> bytes:
+    if SECRET.exists():
+        return SECRET.read_bytes()
+    s = secrets.token_bytes(32)
+    DATA.mkdir(exist_ok=True)
+    fd = os.open(SECRET, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
+    with os.fdopen(fd, "wb") as f:
+        f.write(s)
+    return s
+
+
+def migrate_legacy():
+    """one-time: single-password era -> users.json + per-user history files."""
+    cred = DATA / "credentials.json"
+    if not USERS.exists() and cred.exists():
+        d = json.loads(cred.read_text())
+        save({"admin": {"salt": d["salt"], "hash": d["hash"], "created": time.time()}})
+        cred.unlink()
+    old_hist = DATA / "history.json"
+    if not (DATA / "history" / "admin.json").exists() and old_hist.exists():
+        (DATA / "history").mkdir(exist_ok=True)
+        old_hist.rename(DATA / "history" / "admin.json")
+
+
+def load() -> dict:
+    try:
+        return json.loads(USERS.read_text())
+    except (FileNotFoundError, json.JSONDecodeError):
+        return {}
+
+
+def save(users: dict):
+    DATA.mkdir(exist_ok=True)
+    # ponytail: mode 0600 on create; won't tighten an existing file
+    fd = os.open(USERS, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
+    with os.fdopen(fd, "w") as f:
+        json.dump(users, f, indent=1)
+
+
+def add(username: str, password: str):
+    u = username.lower()
+    if not NAME_RE.match(u):
+        raise ValueError("username: 3-32 chars, only a-z 0-9 _ -")
+    if len(password) < 8:
+        raise ValueError("password: min 8 chars")
+    users = load()
+    if u in users:
+        raise ValueError("username already taken")
+    salt = secrets.token_bytes(16)
+    users[u] = {"salt": salt.hex(),
+                "hash": hashlib.pbkdf2_hmac("sha256", password.encode(), salt, ITER).hex(),
+                "created": time.time()}
+    save(users)
+
+
+def verify(username: str, password: str) -> bool:
+    d = load().get(username.lower())
+    if not d:
+        return False
+    h = hashlib.pbkdf2_hmac("sha256", password.encode(),
+                            bytes.fromhex(d["salt"]), d.get("iter", ITER))
+    return secrets.compare_digest(h.hex(), d["hash"])
+
+
+def remove(username: str):
+    u = username.lower()
+    users = load()
+    users.pop(u, None)
+    save(users)
+    (DATA / "history" / f"{u}.json").unlink(missing_ok=True)
+
+
+if __name__ == "__main__":
+    import sys
+    cmd = sys.argv[1] if len(sys.argv) > 1 else ""
+    if cmd == "add" and len(sys.argv) > 2:
+        name = sys.argv[2]
+        pw = getpass.getpass(f"Password for {name} (min 8 chars): ")
+        if pw != getpass.getpass("Again: "):
+            raise SystemExit("passwords did not match")
+        try:
+            add(name, pw)
+        except ValueError as e:
+            raise SystemExit(str(e))
+        print(f"added user {name.lower()}")
+    elif cmd == "rm" and len(sys.argv) > 2:
+        remove(sys.argv[2])
+        print(f"removed {sys.argv[2].lower()} (incl. history)")
+    elif cmd == "list":
+        for u in sorted(load()):
+            print(u)
+    else:
+        print(__doc__)
+        raise SystemExit(2)