Agent: resolve "today" in the browser's timezone, not hardcoded CR

The CR-hardcoded today broke two scenarios: the owner traveling, and
any future non-CR user. Now the provider sends the browser's IANA
timezone (X-Client-Timezone) with every CopilotKit request — the
runtime forwards x-* headers to the agent on its own — and the backend
binds it to a per-request ContextVar next to the DB session.
get_current_date and the future-cuota bounds use it; the tool also
reports the timezone so the model can echo it. Unknown or absent zones
(n8n posts, tests) fall back to Costa Rica; comma-joined duplicate
header values are tolerated.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/agent/agent.py

@@ -21,9 +21,10 @@ Context you can rely on:
   qualifiers, assume they mean the calendar month unless they mention
   "cycle", "corte", or their credit card.
 - You do NOT have a reliable clock, and the server runs in UTC while the
-  user lives in Costa Rica (UTC-6). Whenever the question involves a
-  relative date — "hoy", "ayer", "este mes", "este ciclo", "el año
-  pasado" — call get_current_date FIRST and derive ranges from its answer.
+  user may be anywhere (their browser reports their timezone per request).
+  Whenever the question involves a relative date — "hoy", "ayer", "este
+  mes", "este ciclo", "el año pasado" — call get_current_date FIRST and
+  derive ranges from its answer.
 - Amounts are stored as raw numbers in their native currency (see `currency`
   field on transactions/accounts). Tools that return `total_crc` are already
   converted; tools that return per-transaction amounts are NOT.

backend/app/agent/tools.py

@@ -41,7 +41,7 @@ from app.services.budget_projection import (
     get_cycle_range,
 )
 from app.services import exchange_rate as fx
-from app.timeutil import today_cr
+from app.timeutil import client_tz, today_client
 from app.services.exchange_rate import (
     get_converted_amount_expr,
     get_current_rate,
@@ -145,8 +145,8 @@ def get_recent_transactions(
         ),
         # Tasa Cero generates future-dated cuotas; "recent" means already
         # billed (same rule as /transactions/recent). Bound is end of the
-        # user's today, Costa Rica time.
-        Transaction.date < datetime.combine(today_cr() + timedelta(days=1), time.min),
+        # user's today in their request timezone (CR fallback).
+        Transaction.date < datetime.combine(today_client() + timedelta(days=1), time.min),
     )
     if source:
         q = q.where(Transaction.source == TransactionSource(source))
@@ -519,7 +519,7 @@ def get_daily_spending(
             Transaction.date >= datetime.fromisoformat(start_date),
             Transaction.date < datetime.fromisoformat(end_date),
             # Future-dated Tasa Cero cuotas are not money already spent.
-            Transaction.date < datetime.combine(today_cr() + timedelta(days=1), time.min),
+            Transaction.date < datetime.combine(today_client() + timedelta(days=1), time.min),
         )
         .group_by(func.date(Transaction.date))
         .order_by(func.date(Transaction.date))
@@ -531,12 +531,12 @@ def get_daily_spending(
 
 
 def get_current_date() -> dict:
-    """Today's date in the user's timezone (Costa Rica, UTC-6) and the
-    active credit-card billing cycle. ALWAYS call this before resolving any
-    relative date reference — 'hoy', 'ayer', 'este mes', 'este ciclo',
-    'el ciclo pasado' — the server clock and your own assumptions about
-    today are unreliable."""
-    today = today_cr()
+    """Today's date in the user's own timezone (sent by their browser;
+    Costa Rica fallback) and the active credit-card billing cycle. ALWAYS
+    call this before resolving any relative date reference — 'hoy', 'ayer',
+    'este mes', 'este ciclo', 'el ciclo pasado' — the server clock and your
+    own assumptions about today are unreliable."""
+    today = today_client()
     # get_cycle_range(y, m) is the cycle STARTING on the 18th of m; before
     # the 18th we are still in the cycle that started last month.
     if today.day >= 18:
@@ -549,6 +549,7 @@ def get_current_date() -> dict:
     return {
         "date": today.isoformat(),
         "weekday": today.strftime("%A"),
+        "timezone": str(client_tz()),
         "cycle_year": cycle_year,
         "cycle_month": cycle_month,
         "cycle_range": [start.date().isoformat(), end.date().isoformat()],