[FEATURE]: Add persistent transcription history with reusable insights viewer

### Feature and its Use Cases

## Overview

Currently, transcriptions and AI-generated insights (summary, symptoms, medicines) are not persisted. Users lose all data after closing the app.

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## Problem

- No history of past recordings
- No way to revisit medical insights
- Poor real-world usability

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## 💡 Proposed Solution

Implement a local persistence layer to store transcription history:

### Features:
- Save transcript, summary, symptoms, medicines, timestamp
- Retrieve and display past records
- Reuse MedicalInsightsScreen for viewing

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## Suggested Changes

- Add `TranscriptionHistoryModel`
- Add `LocalStorageService` using SharedPreferences
- Update `TranscriptionController` to save history
- Create `HistoryScreen`

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## Expected Outcome

- Users can revisit previous medical conversations
- App becomes usable beyond single session
- Improved UX and product value

### Additional Context

_No response_

### Code of Conduct

- [x] I have joined the [Discord server](https://discord.gg/hjUhu33uAn) and will post updates there
- [x] I have searched existing issues to avoid duplicates