chore(ci): add gitsecrets configuration and ignore file

Initialize GitSecrets addon configuration with project analysis metadata. Add .gitsecrets-ignore file marking password-assignment detection in BuyMeACoffeeExtensions.cs as false positive.

.gitsecrets-ignore

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+# GitSecrets Ignore File
+# This file tracks false positives identified by AI evaluation or manually marked.
+# Each line is a JSON object with the following fields:
+# - contentHash: SHA256 hash prefix of the secret content
+# - patternId: The pattern that detected this secret
+# - filePath: Relative path where the secret was found
+# - reason: Why this was marked as a false positive
+# - confidence: AI confidence level (if from AI evaluation)
+# - addedAt: Timestamp when this entry was added
+#
+# You can safely commit this file to share false positive markers with your team.
+# To remove an entry, simply delete the corresponding line.
+
+{"contentHash":"57ca47aa82486958","patternId":"password-assignment","filePath":"..\\..\\..\\AppData\\Local\\GitCaddy\\app-4.7.1\\BuyMeCofee.Maui\\BuyMeACoffeeExtensions.cs","reason":"Manually marked as false positive","addedAt":1772602630533}

.gitsecretsconfig

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+{
+  "version": 1,
+  "analyzedAt": 1772602627117,
+  "project": {
+    "type": "unknown"
+  },
+  "vaultSdk": {
+    "installed": false,
+    "usageLocations": []
+  },
+  "recommendedApproach": "unknown"
+}