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

[Shweta-281]

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.

---

Problem

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

---

💡 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

---

Suggested Changes

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

---

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

• I have joined the Discord server and will post updates there
• I have searched existing issues to avoid duplicates