Feature/delta team/epic r04 (#7)

## Summary

epic r04 - begin refactor

## Change Type

- [x] Cowork feature
- [ ] Bug fix
- [ ] Core AI contribution
- [ ] Test / hardening
- [ ] Performance
- [ ] Documentation

## Related Work

Cowork Task:

Core Repo: http://34.143.229.138/gitea-admin/fsg-ai-core-assets

Core AI Issue:

Core Task:

Related PR:

## Scope

What is intentionally included?

What is intentionally NOT included?

## Validation

- [ ] Unit tests
- [ ] Integration tests
- [ ] Manual verification
- [ ] Regression check

Commands / evidence:

## Security Impact

Permission / credential / network / customer data impact:

## Compatibility

- [ ] No breaking change
- [ ] Breaking change documented

## Reviewer Notes

Anything Cowork reviewers should pay attention to.

---------

Co-authored-by: Anh Tran Nguyen Minh <anhtnm1@fpt.com>
Co-authored-by: Huong Le Thi Thien <huongltt35@fpt.com>
Co-authored-by: Nam Pham Dinh Thanh <nampdt@fpt.com>
Co-authored-by: Vu Dam Tuan <vudt15@fpt.com>
Co-authored-by: Hiep Ha Van <hiephv3@fpt.com>
Co-authored-by: Lam Hoang Van <lamhv7@fpt.com>
Reviewed-on: #7
Co-authored-by: Duy Le Huu <duylh19@fpt.com>

core/usage_cost.py

@@ -0,0 +1,102 @@
+"""Bảng giá và quy đổi token thành tiền — R09-T02.
+
+Tách khỏi ``usage_tracker.py``: ghi nhận mức dùng và tính tiền là hai việc
+khác nhau. Bảng giá đổi theo nhà cung cấp, cách ghi nhận thì không.
+"""
+from __future__ import annotations
+
+import json
+import threading
+from datetime import date, datetime
+from pathlib import Path
+from typing import Any, Dict, List, Optional
+from ..config import CONFIG_DIR
+from . import model_pricing as mp
+
+DEFAULT_PRICING = {
+    "price_per_mtok_in_usd": 0.5,     # USD per 1M input tokens (flat fallback rate)
+    "price_per_mtok_out_usd": 1.5,    # USD per 1M output tokens
+    "price_per_mtok_cache_usd": 0.1,  # USD per 1M cached tokens
+    "currency": "USD",                # display currency: USD | VND | JPY
+    "usd_to_vnd": 25000.0,
+    "usd_to_jpy": 150.0,
+    # Per-model price table (USD / 1M tokens): {model: {"in","out","cache"}}.
+    # Events whose model has an entry are costed with ITS rates; everything
+    # else falls back to the flat price_per_mtok_* rates above. Edited in the
+    # Monitoring Overview's pricing table.
+    "model_prices": {},
+    # Reference URL of the price list the table was filled from (set in
+    # Settings; shown as a link beside the table — informational only, the
+    # app never scrapes it).
+    "pricing_url": "",
+}
+
+_CURRENCY_FMT = {"USD": ("$", 4), "VND": ("₫", 0), "JPY": ("¥", 1)}
+
+SUPPORTED_CURRENCIES = tuple(_CURRENCY_FMT)
+
+def cost_usd(summary: Dict[str, Any], pricing: Dict[str, Any]) -> Dict[str, float]:
+    """Quy số token thành tiền (USD) theo bảng đơn giá, tách riêng vào/ra/cache."""
+    p = {**DEFAULT_PRICING, **(pricing or {})}
+    return {
+        "in": summary.get("in", 0) / 1e6 * float(p["price_per_mtok_in_usd"]),
+        "out": summary.get("out", 0) / 1e6 * float(p["price_per_mtok_out_usd"]),
+        "cache": summary.get("cache", 0) / 1e6 * float(p["price_per_mtok_cache_usd"]),
+    }
+
+def cost_usd_events(events: List[Dict[str, Any]], pricing: Dict[str, Any]) -> Dict[str, float]:
+    """Per-bucket USD cost computed EVENT BY EVENT so the per-model price
+    table applies: an event whose ``model`` has an entry in
+    ``pricing["model_prices"]`` is costed with that model's own rates; any
+    other event uses the flat ``price_per_mtok_*`` rates. With an empty
+    table this equals ``cost_usd(summarize(events), pricing)`` exactly."""
+    p = {**DEFAULT_PRICING, **(pricing or {})}
+    table = p.get("model_prices") or {}
+    flat = {"in": float(p["price_per_mtok_in_usd"]),
+            "out": float(p["price_per_mtok_out_usd"]),
+            "cache": float(p["price_per_mtok_cache_usd"])}
+    out = {"in": 0.0, "out": 0.0, "cache": 0.0}
+    for e in events:
+        rates = table.get(e.get("model", "")) or {}
+        for bucket in ("in", "out", "cache"):
+            try:
+                rate = float(rates.get(bucket, flat[bucket]))
+            except (TypeError, ValueError):
+                rate = flat[bucket]
+            out[bucket] += e.get(bucket, 0) / 1e6 * rate
+    return out
+
+def format_cost(usd: float, pricing: Dict[str, Any], digits: Optional[int] = None) -> str:
+    """Format a USD amount in the display currency. ``digits`` caps the number
+    of decimal places (e.g. ``digits=2`` for the Total cost / Budget cards, so
+    USD shows $1.23 not the default up-to-4 $1.2345) — never ADDS decimals to a
+    currency that uses fewer (VND stays whole, JPY one place)."""
+    p = {**DEFAULT_PRICING, **(pricing or {})}
+    cur = p.get("currency", "USD")
+    rate = {"USD": 1.0, "VND": float(p["usd_to_vnd"]), "JPY": float(p["usd_to_jpy"])}.get(cur, 1.0)
+    symbol, cur_digits = _CURRENCY_FMT.get(cur, ("$", 2))
+    if digits is not None:
+        cur_digits = min(cur_digits, digits)
+    value = usd * rate
+    return f"{symbol}{value:,.{cur_digits}f}"
+
+def format_cost_compact(usd: float, pricing: Dict[str, Any]) -> str:
+    """Compact cost format for the Dashboard chart's y-axis/endpoint labels —
+    always 2 decimals (not format_cost's up-to-4 for USD) and abbreviated with
+    K/M above 1,000/1,000,000, same convention as ``fmt_tokens``. The chart's
+    y-axis label box is narrow; the longer full-precision string used to
+    overflow it, visually clipping/obscuring the leading currency symbol."""
+    p = {**DEFAULT_PRICING, **(pricing or {})}
+    cur = p.get("currency", "USD")
+    rate = {"USD": 1.0, "VND": float(p["usd_to_vnd"]), "JPY": float(p["usd_to_jpy"])}.get(cur, 1.0)
+    symbol, _digits = _CURRENCY_FMT.get(cur, ("$", 2))
+    value = usd * rate
+    sign = "-" if value < 0 else ""
+    value = abs(value)
+    if value >= 1_000_000:
+        body = f"{value / 1_000_000:,.2f}M"
+    elif value >= 1_000:
+        body = f"{value / 1_000:,.2f}K"
+    else:
+        body = f"{value:,.2f}"
+    return f"{sign}{symbol}{body}"