Fix bugs, data integrity, and cache busting

- models.py: add UniqueConstraint(user_id, date) to flock_history so
  duplicate flock entries for the same day are rejected at the DB level
- main.py: v2.3 migration applies the new unique constraint to existing
  installs at startup
- login.html: update register form minlength and placeholder from 6 to 10
  characters to match backend; add specific 429 error message so rate-
  limited users see "Too many attempts — please wait a minute" instead of
  a generic failure
- auth.js: update settings modal password input minlength from 6 to 10
- summary.js: fix CSV export truncation — pass limit=10000 so users with
  more than 500 days of data get a complete export; read chart border color
  from --green CSS variable instead of hardcoded hex
- All HTML files: bump JS version params to ?v=4 so browsers discard
  cached copies of files changed across recent sessions (api.js, auth.js,
  dashboard.js, history.js, log.js, flock.js, budget.js, summary.js,
  admin.js)
- .env.example: add password strength guidance for MySQL and admin vars

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

nginx/html/js/summary.js

@@ -18,7 +18,8 @@ function buildChart(rows) {
     const labels  = display.map(r => r.month_label);
     const data    = display.map(r => r.total_eggs);
 
-    const ctx = document.getElementById('monthly-chart').getContext('2d');
+    const ctx   = document.getElementById('monthly-chart').getContext('2d');
+    const green = getComputedStyle(document.documentElement).getPropertyValue('--green').trim();
     if (monthlyChart) monthlyChart.destroy();
 
     monthlyChart = new Chart(ctx, {
@@ -28,7 +29,7 @@ function buildChart(rows) {
             datasets: [{
                 data,
                 backgroundColor: 'rgba(61,107,79,0.75)',
-                borderColor:     '#3d6b4f',
+                borderColor:     green,
                 borderWidth: 1,
                 borderRadius: 4,
             }],
@@ -100,7 +101,7 @@ async function exportCSV() {
 
     try {
         const [eggsData, flockAll, feedData] = await Promise.all([
-            API.get('/api/eggs'),
+            API.get('/api/eggs?limit=10000'),
             API.get('/api/flock'),
             API.get('/api/feed'),
         ]);