fix: Leads page cleanup — remove tabs, checkboxes, inline header

- Remove New/My Leads/All Leads tabs — redundant now that contacts
  are on a separate page; all leads shown as a flat list
- Remove row checkboxes (selectionMode="none") — bulk actions weren't
  wired to any backend and confused QA
- Move Search + Columns + Export into the header row alongside the
  title — cleaner single-row layout
- Remove BulkActionBar + AssignModal + WhatsAppSendModal + MarkSpamModal
  imports and JSX — dead code without checkboxes
- LeadTable: new selectionMode prop (default "multiple" for back-compat)
- Same cleanup on Contacts page (no checkboxes)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.claude/settings.local.json

@@ -0,0 +1,16 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(ps -eo pid,pcpu,rss,comm -r)",
+      "Bash(awk 'NR<=20{printf \"%-8s %-8s %-10s %s\\\\n\", $1, $2, $3/1024 \"MB\", $4}')",
+      "Bash(top -l 1 -o cpu -n 15 -stats pid,command,cpu,mem,th)",
+      "Bash(vm_stat)",
+      "Bash(sysctl hw.memsize)",
+      "Bash(awk '{print \"Total RAM: \" $2/1024/1024/1024 \" GB\"}')",
+      "Bash(ps aux:*)",
+      "Bash(pmset -g thermlog)",
+      "Bash(sudo powermetrics:*)",
+      "Bash(sysctl machdep.xcpm.cpu_thermal_level)"
+    ]
+  }
+}