feat: remove FPX, add UK charity persona features

- Remove FPX payment rail entirely (Malaysian, not UK)
- Add volunteer portal (/v/[code]) with live pledge tracking
- Add public event page (/e/[slug]) with progress bar + social proof
- Add fundraiser leaderboard (/dashboard/events/[id]/leaderboard)
- Add WhatsApp share buttons on confirmation, bank instructions, volunteer view
- Enhanced Gift Aid UX with +25% bonus display and HMRC declaration text
- Gift Aid report export (HMRC-ready CSV filter)
- Volunteer view link + WhatsApp share on QR code cards
- Updated home page: 4 personas, 3 UK payment rails, 8 features
- Public event API endpoint with privacy-safe donor name truncation
- Volunteer API with stats, conversion rate, auto-refresh

justfile

@@ -1,4 +1,5 @@
 set dotenv-load := true
+set shell := ["pwsh", "-NoProfile", "-Command"]
 
 default:
     @just --list
@@ -87,20 +88,16 @@ ext-theme-cycler:
 
 # Open pi with one or more stacked extensions in a new terminal: just open minimal tool-counter
 open +exts:
-    #!/usr/bin/env bash
-    args=""
-    for ext in {{exts}}; do
-        args="$args -e extensions/$ext.ts"
-    done
-    cmd="cd '{{justfile_directory()}}' && pi$args"
-    escaped="${cmd//\\/\\\\}"
-    escaped="${escaped//\"/\\\"}"
-    osascript -e "tell application \"Terminal\" to do script \"$escaped\""
+    #!/usr/bin/env pwsh
+    $args_str = ""
+    foreach ($ext in "{{exts}}".Split(" ")) { $args_str += " -e extensions/$ext.ts" }
+    $cmd = "cd '{{justfile_directory()}}'; pi$args_str"
+    Start-Process wt -ArgumentList "pwsh", "-NoExit", "-Command", $cmd
 
 # Open every extension in its own terminal window
 all:
     just open pi
-    just open pure-focus 
+    just open pure-focus
     just open minimal theme-cycler
     just open cross-agent minimal
     just open purpose-gate minimal