feat: Add sidebar unread counts for filters (CW-7262) (#14726)

## Description

Extends the conversation unread-count system so the left sidebar can
show unread badges for Mentions, Participating, Unattended, and saved
conversation folders. Folder badges reuse the existing `custom_filters`
conversation filter semantics, store user-scoped Redis sets lazily, and
skip unsupported folder filters so invalid saved folders continue to
render without a badge. The Unattended badge counts all visible unread
open conversations that match the existing unattended conversation
scope.

Closes
-
[CW-7262](https://linear.app/chatwoot/issue/CW-7262/unread-counts-for-filters-folders)

## What changed

- Added user-scoped unread-count Redis keys and cache builders for
mentions, participating conversations, unattended conversations, and
saved folder filters.
- Reused `Conversations::FilterService` through a relation-returning
path so folder counts match the folder conversation list behavior.
- Invalidated user filter caches from mention, participant,
custom-filter, and relevant conversation update events.
- Extended the unread-count endpoint payload and sidebar Vuex/sidebar
rendering for the new badge counts, including the Unattended sidebar
item.
- Added Ruby, Enterprise, request, listener, and frontend store coverage
for the new unread-count dimensions.

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

- Created local validation folders for `john@acme.inc` and confirmed the
unread-count payload includes open, resolved, and high-priority folder
badges while excluding the invalid unsupported folder.
- Added coverage for the Unattended badge rule: all visible unread open
conversations matching `Conversation.unattended`.
- Ran focused unread-count Ruby specs, including service, listener,
request, and Enterprise counter coverage.
- Ran frontend unread-count store specs.
- Ran RuboCop on the touched Ruby files.
- Ran ESLint through the project script; it completed with warnings in
existing unrelated files and no errors.

<img width="369" height="525" alt="Screenshot 2026-06-13 at 10 51 39 PM"
src="https://github.com/user-attachments/assets/36b1d2c4-dac1-4f6f-9c0e-7ef5a6cc2975"
/>

## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [x] Documentation changes are not required for this internal
unread-count behavior
- [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
- [x] No dependent downstream changes are required

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/javascript/dashboard/i18n/locale/en/settings.json

@@ -316,6 +316,16 @@
     "MENTIONED_CONVERSATIONS": "Mentions",
     "PARTICIPATING_CONVERSATIONS": "Participating",
     "UNATTENDED_CONVERSATIONS": "Unattended",
+    "UNREAD_COUNT_TOOLTIP": {
+      "ALL": "Total unread conversations",
+      "INBOX": "Total unread conversations in this inbox",
+      "LABEL": "Total unread conversations in this label",
+      "TEAM": "Total unread conversations in this team",
+      "FOLDER": "Total unread conversations in this folder",
+      "MENTIONS": "Unread conversations where you were mentioned",
+      "PARTICIPATING": "Unread conversations you're participating in",
+      "UNATTENDED": "Unread unattended conversations"
+    },
     "REPORTS": "Reports",
     "SETTINGS": "Settings",
     "CONTACTS": "Contacts",