Auto-breakpoint at PRG entry point on connect

## Description

When connecting to VICE with a PRG already loaded, it would be useful to automatically set a breakpoint at the program's entry point so the user lands directly at their code.

## Proposed implementation

- After `populate_initial_state()`, check if a PRG load address is known (either from Ghidra's program info or from the launcher parameter)
- If known, set an execution breakpoint at that address via `checkpoint_set`
- Optionally make this configurable via a launcher parameter (`OPT_BREAK_AT_ENTRY`)

## Depends on

Potentially #3 (auto-load PRG) if the entry point comes from the loaded file.

## Why this matters

Saves the user from manually navigating to their code's entry point and setting a breakpoint every time they reconnect.