chore: Clean up report & knowledge base policies (#11234)

- Removes the portal_members table and all associated records
- Updates policies to use custom roles with knowledge_base_manage
permission
- Updates controllers, models, and views to work without portal
membership
- Adds tests for the new permission model

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.0].define(version: 2025_03_26_034635) do
+ActiveRecord::Schema[7.0].define(version: 2025_04_02_233933) do
   # These extensions should be enabled to support this database
   enable_extension "pg_stat_statements"
   enable_extension "pg_trgm"
@@ -871,15 +871,6 @@ ActiveRecord::Schema[7.0].define(version: 2025_03_26_034635) do
     t.datetime "updated_at", null: false
   end
 
-  create_table "portal_members", force: :cascade do |t|
-    t.bigint "portal_id"
-    t.bigint "user_id"
-    t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
-    t.index ["portal_id", "user_id"], name: "index_portal_members_on_portal_id_and_user_id", unique: true
-    t.index ["user_id", "portal_id"], name: "index_portal_members_on_user_id_and_portal_id", unique: true
-  end
-
   create_table "portals", force: :cascade do |t|
     t.integer "account_id", null: false
     t.string "name", null: false