fix: require Python 3.10+ in edict startup scripts

[njiangk]

Summary

• make start.sh automatically select a Python 3.10+ interpreter
• pass the selected interpreter through to scripts/run_loop.sh
• update README to match the project's actual Python requirement

Problem

The repository README says Python 3.9+ is supported, and start.sh launches the dashboard with plain python3. On macOS systems where python3 is still 3.9, startup fails immediately because the codebase already uses Python 3.10+ syntax such as pathlib.Path | None.

Fix

This PR aligns the startup path and docs with the real runtime requirement:

• start.sh now looks for EDICT_PYTHON, then python3.12, python3.11, python3.10, and finally python3, accepting the first interpreter that is 3.10+
• the selected interpreter is exported and reused by scripts/run_loop.sh
• README now states Python 3.10+

Reproduction

On a machine with python3 = 3.9.x, run:

chmod +x start.sh && ./start.sh

Startup fails during import with:

TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

Validation

• verified startup succeeds with Python 3.11
• verified dashboard serves successfully on http://127.0.0.1:7891/
• verified the refresh loop uses the same interpreter selection path