🎨 Palette: Improve JSON parse error visibility

[sl4m3]

💡 What: Replaced a bare except: block in the CLI transcript sync logic with an explicit except json.JSONDecodeError as e: and added a formatted, color-coded rich console warning.
🎯 Why: Previously, invalid JSON lines in the sync transcript were silently ignored, returning an empty dictionary. This invisible failure obscured corrupted data and caused debugging frustration for users/developers. The explicit warning provides immediate, actionable feedback.
📸 Before/After:
Before: Silent failure.
After: Outputs [yellow]Warning: Failed to parse context JSON: [error details][/yellow] to the console.
♿ Accessibility: Uses the existing color-coded (yellow) and semantic ("Warning") conventions of the CLI's rich formatting to ensure the error state is clear.

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PR created automatically by Jules for task 12643695223778339595 started by @sl4m3

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