feat: add locale formatting config and update notebook outputs

Add configurable locale/display formatting environment variables
(`PALLADIUM_CURRENCY_SYMBOL`, `PALLADIUM_THOUSANDS_SEP`,
`PALLADIUM_DECIMAL_SEP`) to support regional number formatting in the
Streamlit app. Update `.env.example` with documentation for these new
variables.

Also refresh `00_setup.ipynb` with current execution outputs reflecting
a live Athena connection with report templates, a selected client
(Global Guardian Insurance, ID=2), and resolved NameError in assumption
override cells.

app/locale.py

@@ -0,0 +1,87 @@
+"""
+Locale / formatting settings for the Palladium Streamlit app.
+
+All settings are read from environment variables (via .env) so the same
+codebase can be deployed for different regions without code changes.
+
+Environment variables
+---------------------
+PALLADIUM_CURRENCY_SYMBOL   Default: "$"
+    Prefix shown before monetary values (e.g. "$", "€", "£", "CAD ").
+
+PALLADIUM_THOUSANDS_SEP     Default: ","
+    Thousands separator used in number display (e.g. "," for Americas,
+    "." for continental Europe, " " for some locales).
+
+PALLADIUM_DECIMAL_SEP       Default: "."
+    Decimal separator (e.g. "." for Americas/UK, "," for continental Europe).
+
+Note: Streamlit's NumberColumn ``format`` uses printf-style strings.
+The ``%,`` flag (thousands separator) is supported in Streamlit ≥ 1.31.
+For non-standard separators (e.g. European "." thousands / "," decimal)
+the values are pre-formatted as strings and displayed in TextColumns.
+"""
+
+from __future__ import annotations
+
+import os
+
+
+def _env(key: str, default: str) -> str:
+    return os.environ.get(key, default).strip()
+
+
+# ---------------------------------------------------------------------------
+# Resolved settings (read once at import time; restart app to pick up changes)
+# ---------------------------------------------------------------------------
+CURRENCY_SYMBOL: str = _env("PALLADIUM_CURRENCY_SYMBOL", "$")
+THOUSANDS_SEP: str = _env("PALLADIUM_THOUSANDS_SEP", ",")
+DECIMAL_SEP: str = _env("PALLADIUM_DECIMAL_SEP", ".")
+
+# True when the locale uses standard printf-compatible separators
+# (i.e. "," thousands + "." decimal — the C/POSIX default).
+# When False, we pre-format values as strings instead of relying on printf.
+_STANDARD_LOCALE: bool = THOUSANDS_SEP == "," and DECIMAL_SEP == "."
+
+
+def currency_fmt() -> str:
+    """Return a Streamlit NumberColumn ``format`` string for currency.
+
+    For standard locales returns e.g. ``"$%,.0f"`` (thousands-separated,
+    no decimal places).  For non-standard locales returns ``"%s"`` and
+    callers should use :func:`fmt_currency` to pre-format the value.
+    """
+    if _STANDARD_LOCALE:
+        return f"{CURRENCY_SYMBOL}%,.0f"
+    return "%s"
+
+
+def pct_fmt() -> str:
+    """Return a Streamlit NumberColumn ``format`` string for percentages.
+
+    Stores the value as a fraction (0–1) and displays as e.g. ``"20.00%"``.
+    Streamlit's ``%%`` in format strings renders a literal ``%``.
+    """
+    if _STANDARD_LOCALE:
+        return "%.2f%%"
+    return "%s"
+
+
+def fmt_currency(value: float) -> str:
+    """Format *value* as a currency string using the configured locale."""
+    if _STANDARD_LOCALE:
+        return f"{CURRENCY_SYMBOL}{value:,.0f}"
+    # Non-standard: build manually
+    integer_part = f"{int(abs(value)):,}".replace(",", THOUSANDS_SEP)
+    sign = "-" if value < 0 else ""
+    return f"{sign}{CURRENCY_SYMBOL}{integer_part}"
+
+
+def fmt_pct(value: float) -> str:
+    """Format *value* (0–1 fraction) as a percentage string."""
+    pct = value * 100
+    if _STANDARD_LOCALE:
+        return f"{pct:.2f}%"
+    integer_part = f"{int(pct)}"
+    decimal_part = f"{abs(pct) % 1:.2f}"[1:]  # ".xx"
+    return f"{integer_part}{DECIMAL_SEP}{decimal_part[1:]}%"