feat: Add POST /flush-cache endpoint to clear all cached data and reset timers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app.py

@@ -7,7 +7,7 @@ import os
 import io
 import qrcode
 import logging
-from flask import Flask, render_template, g, send_file, request
+from flask import Flask, render_template, g, send_file, request, jsonify
 
 # Configure logging, allowing override via LOG_LEVEL environment variable
 log_level = os.environ.get("LOG_LEVEL", "INFO").upper()
@@ -23,7 +23,7 @@ from config import (
 )
 from attendance import get_members_with_fees, get_junior_members_with_fees, ADULT_MERGED_MONTHS, JUNIOR_MERGED_MONTHS
 from match_payments import reconcile, fetch_sheet_data, fetch_exceptions, normalize
-from cache_utils import get_sheet_modified_time, read_cache, write_cache, _LAST_CHECKED
+from cache_utils import get_sheet_modified_time, read_cache, write_cache, _LAST_CHECKED, flush_cache
 
 def get_cached_data(cache_key, sheet_id, fetch_func, *args, serialize=None, deserialize=None, **kwargs):
     mod_time = get_sheet_modified_time(cache_key)
@@ -108,6 +108,11 @@ def index():
     # Redirect root to /adults for convenience while there are no other apps
     return '<meta http-equiv="refresh" content="0; url=/adults" />'
 
+@app.route("/flush-cache", methods=["POST"])
+def flush_cache_endpoint():
+    deleted = flush_cache()
+    return jsonify({"status": "ok", "deleted_files": deleted})
+
 @app.route("/fees")
 def fees():
     attendance_url = f"https://docs.google.com/spreadsheets/d/{ATTENDANCE_SHEET_ID}/edit"