chore: add HACS default prerequisites (CI validation, issue_tracker, brand icon)

Groundwork for submitting to hacs/default:
- .github/workflows/validate.yml running hassfest + hacs/action validation
  on push/PR/schedule, matching the standard custom-components/blueprint
  pattern required for HACS default submission.
- manifest.json: added the required "issue_tracker" field.
- custom_components/splitwise/brand/icon.txt: local brand icon fallback
  (mdi:cash, matching the sensor's existing icon) using HA's local brand
  directory support, so a custom-designed PNG can be swapped in later
  without needing a home-assistant/brands PR first.

Author: sriramsv

.github/workflows/validate.yml

@@ -0,0 +1,37 @@
+name: Validate
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: "0 0 * * *"
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+permissions: {}
+
+jobs:
+  hassfest: # https://developers.home-assistant.io/blog/2020/04/16/hassfest
+    name: Hassfest validation
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout the repository
+        uses: actions/checkout@v4
+
+      - name: Run hassfest validation
+        uses: home-assistant/actions/hassfest@master
+
+  hacs: # https://github.com/hacs/action
+    name: HACS validation
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout the repository
+        uses: actions/checkout@v4
+
+      - name: Run HACS validation
+        uses: hacs/action@main
+        with:
+          category: integration

custom_components/splitwise/brand/icon.txt

@@ -0,0 +1 @@
+mdi:cash

custom_components/splitwise/manifest.json

@@ -2,10 +2,11 @@
     "domain": "splitwise",
     "name": "Splitwise",
     "documentation": "https://github.com/sriramsv/custom_component_splitwise",
+    "issue_tracker": "https://github.com/sriramsv/custom_component_splitwise/issues",
     "dependencies": ["application_credentials"],
     "codeowners": ["sriramsv"],
     "requirements": ["splitwise==3.0.0"],
     "iot_class": "cloud_polling",
     "config_flow": true,
-    "version": "0.2.6"
+    "version": "0.2.7"
   }

hacs.json

@@ -2,6 +2,6 @@
     "name": "Splitwise Sensor",
     "domains": ["sensor"],
     "country": ["US"],
-    "version": "0.2.6",
+    "version": "0.2.7",
     "render_readme": true
   }