feat: Polar license key integration and dashboard UI improvements

- Add license activation flow: server validates/activates keys via Polar SDK
- Auto-activate from Polar checkout redirect (checkout_id in URL)
- Gate dashboard behind license activation (redirect to /activate if no plan)
- Preserve redirect URL through login flow for post-purchase activation
- Show plan status badge in sidebar and overview page
- Add account section to settings (email, plan, license key)
- Add svelte-sonner toasts with custom black theme and iconify icons
- Improve validation messages across all forms
- Update API key prefix to droidclaw_
- Add cursor pointer globally for clickable elements
- Support Polar sandbox mode via POLAR_SANDBOX env flag

web/drizzle/meta/_journal.json

@@ -22,6 +22,13 @@
       "when": 1771326794177,
       "tag": "0002_fearless_greymalkin",
       "breakpoints": true
+    },
+    {
+      "idx": 3,
+      "version": "7",
+      "when": 1771429350614,
+      "tag": "0003_familiar_green_goblin",
+      "breakpoints": true
     }
   ]
 }