Fix webhook failing to update plan for pre-existing Supabase users

supabase_admin_invite re-sends a magic link for users who already have
an account (e.g. signed up via attestation before paying) but does not
touch their user_metadata — leaving plan as "free" after purchase.

Fix: add supabase_admin_update_user (PUT /auth/v1/admin/users/{id})
and call it after every invite so user_metadata is always stamped with
the correct plan, name, and stripe_customer_id. Idempotent for new and
returning users.

Also fix waitlist_upsert to use on_conflict=email,plan so the upsert
works for users who already have a waitlist row from attestation,
rather than silently failing on duplicate key.

src/main.el

@@ -415,8 +415,10 @@ fn waitlist_upsert(email: String, name: String, plan: String, source: String, at
     let ua_safe: String = str_replace(str_replace(user_agent,  "\\", "\\\\"), "\"", "\\\"")
     let num_field: String = if member_num > 0 { ",\"member_number\":" + int_to_str(member_num) } else { "" }
     let row: String = "{\"email\":\"" + e_safe + "\",\"name\":\"" + n_safe + "\",\"plan\":\"" + plan + "\",\"source\":\"" + source + "\",\"attestation\":\"" + a_safe + "\",\"user_agent\":\"" + ua_safe + "\"" + num_field + "}"
-    let resp: String = supabase_insert(sb_url, sb_key, "waitlist", row)
-    println("[waitlist] supabase insert -> " + resp)
+    // Use on_conflict=email,plan so existing rows are updated (upsert)
+    // rather than silently failing on duplicate key.
+    let resp: String = supabase_insert(sb_url, sb_key, "waitlist?on_conflict=email,plan", row)
+    println("[waitlist] supabase upsert -> " + resp)
     return ""
 }
 
@@ -1620,6 +1622,19 @@ fn handle_request_inner(method: String, path: String, headers: Map, body: String
                         let _cust_resp: String  = http_post_form_auth(cust_url, cust_body, stripe_auth)
                     }
                 }
+                // Always stamp user_metadata directly via Admin API.
+                // supabase_admin_invite re-sends a magic link for existing users
+                // but does NOT update their user_metadata — so plan stays "free"
+                // for anyone who signed up (attestation, waitlist) before paying.
+                // This PUT is idempotent: safe for both new and returning users.
+                if !str_eq(new_user_id, "") {
+                    let meta_body: String = "{\"user_metadata\":{\"plan\":\"" + plan_safe + "\""
+                        + ",\"name\":\"" + name_safe + "\""
+                        + ",\"stripe_customer_id\":\"" + cid_safe2 + "\""
+                        + ",\"email_verified\":true}}"
+                    let _meta_resp: String = supabase_admin_update_user(wb_sb_url, wb_sb_key, new_user_id, meta_body)
+                    println("[webhook] supabase user_metadata update for " + new_user_id + ": " + _meta_resp)
+                }
             }
 
             // 4. Forward to license API for key provisioning