[TECH DEBT] Chat | USE PKCS7

### 📊 **Priority Level:**
Low

### 📍 **Area/Component:**
`Chat\History\ChatHistoryEncryptor.cs`

### 📝 **Description:**
Unresolved TODO comment in the codebase:

> TODO: USE PKCS7

### 🔍 **Current State:**
The following line is present in `Chat\History\ChatHistoryEncryptor.cs`:

```csharp
cryptoProvider.Padding = PaddingMode.Zeros; // TODO: USE PKCS7
```

### 💡 **Proposed Solution:**
Address the TODO as described in the comment, or remove it if no longer relevant.

### ⚖️ **Impact Assessment:**
#### Performance Impact:
To be assessed when the TODO is picked up.

#### Maintainability Impact:
Unresolved TODOs accumulate as tech debt and obscure the intended final state of the code.

#### Risk of Refactoring:
Low — scoped to the referenced location.

### 📈 **Effort Estimate:**
XS

### 🔗 **Dependencies:**
N/A

### 🖥️ **Additional Notes:**
Created automatically from a bulk TODO audit (todo-list.txt entry #27).

Read Chat\History\ChatHistoryEncryptor.cs at the PaddingMode.Zeros assignment and inspect the surrounding encryption setup to understand the TODO's intent. Confirm whether PKCS7 should replace the current padding or whether the TODO is obsolete, then validate the resulting chat-history encryption behavior with the project's relevant checks.

Written by the indexing model from the issue text.