fix: Change contact_inboxes.source_id to text column (#12882)

## Description

Fixes CW-5961 where IMAP email processing failed with
`ActiveRecord::RecordInvalid: Validation failed: Source is too long
(maximum is 255 characters)` error.

This changes the `contact_inboxes.source_id` column from `string` (255
character limit) to `text` (unlimited) to accommodate long email message
IDs that were causing validation failures.

Fixes CW-5961

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

- Added spec test validating `source_id` values longer than 255
characters (300 chars)
- All existing `contact_inbox_spec.rb` tests pass (7 examples, 0
failures)
- Migration applied successfully with reversible up/down methods
- Verified `source_id` column type changed to `text` with `null: false`
constraint preserved

## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes

db/migrate/20251114173609_change_source_id_to_text.rb

@@ -0,0 +1,9 @@
+class ChangeSourceIdToText < ActiveRecord::Migration[7.1]
+  def up
+    change_column :contact_inboxes, :source_id, :text, null: false
+  end
+
+  def down
+    change_column :contact_inboxes, :source_id, :string, null: false
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.1].define(version: 2025_10_22_152158) do
+ActiveRecord::Schema[7.1].define(version: 2025_11_14_173609) do
   # These extensions should be enabled to support this database
   enable_extension "pg_stat_statements"
   enable_extension "pg_trgm"
@@ -585,7 +585,7 @@ ActiveRecord::Schema[7.1].define(version: 2025_10_22_152158) do
   create_table "contact_inboxes", force: :cascade do |t|
     t.bigint "contact_id"
     t.bigint "inbox_id"
-    t.string "source_id", null: false
+    t.text "source_id", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.boolean "hmac_verified", default: false
@@ -676,7 +676,7 @@ ActiveRecord::Schema[7.1].define(version: 2025_10_22_152158) do
     t.index ["contact_id"], name: "index_conversations_on_contact_id"
     t.index ["contact_inbox_id"], name: "index_conversations_on_contact_inbox_id"
     t.index ["first_reply_created_at"], name: "index_conversations_on_first_reply_created_at"
-    t.index ["identifier", "account_id"], name: "index_conversations_on_identifier_and_account_id" 
+    t.index ["identifier", "account_id"], name: "index_conversations_on_identifier_and_account_id"
     t.index ["inbox_id"], name: "index_conversations_on_inbox_id"
     t.index ["priority"], name: "index_conversations_on_priority"
     t.index ["status", "account_id"], name: "index_conversations_on_status_and_account_id"