feat(dashboard): show Claude usage per day/week instead of per session

Persists per-day token usage (usage_store, ~/.config/wsai/usage.json, survives
restarts) and surfaces it in status as claude_usage.{today,week}. The navbar now
shows two cards — 오늘 토큰 / 주간 토큰 (input+output, with per-card tooltips
breaking down input/output tokens and requests) — replacing the session-only
token count.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

wsai/usage_store.py

@@ -0,0 +1,79 @@
+"""Persisted per-day Claude token usage, for the dashboard's 하루/일주일 사용량.
+
+Each brain call records its token usage into a date bucket
+(``{ "2026-08-22": {"req": n, "in": n, "out": n}, ... }``) persisted to disk so
+the totals survive a restart. ``summary()`` returns today's and the last-7-days
+aggregates. Kept in memory; the file is read once and rewritten on each record.
+
+Path: ``$WSAI_USAGE_PATH`` or ``~/.config/wsai/usage.json`` (disk, never tmpfs).
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import threading
+from datetime import date, timedelta
+from pathlib import Path
+
+_LOCK = threading.Lock()
+_DATA: dict[str, dict[str, int]] | None = None
+_KEEP_DAYS = 90
+
+
+def _path() -> Path:
+    override = os.environ.get("WSAI_USAGE_PATH")
+    return Path(override) if override else (Path.home() / ".config" / "wsai" / "usage.json")
+
+
+def _load() -> dict[str, dict[str, int]]:
+    global _DATA
+    if _DATA is not None:
+        return _DATA
+    try:
+        _DATA = json.loads(_path().read_text(encoding="utf-8"))
+        assert isinstance(_DATA, dict)
+    except (OSError, ValueError, AssertionError):
+        _DATA = {}
+    return _DATA
+
+
+def _write() -> None:
+    p = _path()
+    p.parent.mkdir(parents=True, exist_ok=True)
+    p.write_text(json.dumps(_DATA, ensure_ascii=False), encoding="utf-8")
+
+
+def record(input_tokens: int, output_tokens: int) -> None:
+    """Add one call's usage to today's bucket and persist."""
+    today = date.today().isoformat()
+    with _LOCK:
+        data = _load()
+        b = data.setdefault(today, {"req": 0, "in": 0, "out": 0})
+        b["req"] += 1
+        b["in"] += int(input_tokens or 0)
+        b["out"] += int(output_tokens or 0)
+        # Prune buckets older than _KEEP_DAYS so the file can't grow forever.
+        cutoff = (date.today() - timedelta(days=_KEEP_DAYS)).isoformat()
+        for d in [d for d in data if d < cutoff]:
+            del data[d]
+        _write()
+
+
+def summary() -> dict:
+    """Today's and the last-7-days token totals."""
+    with _LOCK:
+        data = _load()
+        today = date.today().isoformat()
+        week_start = (date.today() - timedelta(days=6)).isoformat()
+        t = data.get(today, {"req": 0, "in": 0, "out": 0})
+        wk = {"req": 0, "in": 0, "out": 0}
+        for d, b in data.items():
+            if d >= week_start:
+                wk["req"] += b.get("req", 0)
+                wk["in"] += b.get("in", 0)
+                wk["out"] += b.get("out", 0)
+    return {
+        "today": {"requests": t.get("req", 0), "input": t.get("in", 0), "output": t.get("out", 0)},
+        "week": {"requests": wk["req"], "input": wk["in"], "output": wk["out"]},
+    }