`hermes update` can crash after a successful code/dependency update when it reaches the post-update config migration prompt:

`Would you like to configure them now? [Y/n]:`

In some interactive terminal contexts, `input()` raises:

```text
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xd0 in position 0: invalid continuation byte
```

This causes the update command to exit with a traceback even though the actual update already completed.

1. Run `hermes update` in an interactive terminal
2. Let the update reach the config migration prompt
3. Answer the prompt in a terminal/input environment that produces malformed decoded stdin bytes
4. Observe crash at:

```python
input("Would you like to configure them now? [Y/n]: ")
```

If terminal input cannot be decoded cleanly, `hermes update` should not crash.

It should:
- print a friendly message
- skip the config migration prompt
- continue successfully
- instruct the user to run `hermes config migrate` manually later

The command exits with a traceback like:

```text
Traceback (most recent call last):
  File "/home/zeus/.local/bin/hermes", line 10, in <module>
    sys.exit(main())
  File "/home/zeus/.hermes/hermes-agent/hermes_cli/main.py", line 8444, in main
    if not hasattr(args, attr):
  File "/home/zeus/.hermes/hermes-agent/hermes_cli/main.py", line 5186, in cmd_update
    _cmd_update_impl(args, gateway_mode=gateway_mode)
  File "/home/zeus/.hermes/hermes-agent/hermes_cli/main.py", line 5578, in _cmd_update_impl
    input("Would you like to configure them now? [Y/n]: ")
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xd0 in position 0: invalid continuation byte
```

Debug report upload failed from this environment:
    - `hermes debug share --lines 300`
    - paste.rs: remote end closed connection without response
    - dpaste.com: SSL handshake timeout

There are already fixes for non-interactive update flows (`isatty()` checks / `EOFError` handling), but this path still does not handle `UnicodeDecodeError` from interactive `input()`.

So the non-interactive case is covered, but an interactive malformed-stdin decoding failure still crashes the update flow.

## Proposed Fix

Wrap the prompt with `UnicodeDecodeError` handling in addition to the existing fallback logic:

```python
try:
    response = input("Would you like to configure them now? [Y/n]: ").strip().lower()
except EOFError:
    response = "n"
except UnicodeDecodeError:
    print("  ℹ Unreadable terminal input — skipping config migration prompt.")
    print("    Run 'hermes config migrate' later to apply any new config/env options.")
    response = "n"
```

Handle `UnicodeDecodeError` alongside the existing `EOFError` fallback in the post-update config migration prompt, and treat it as a non-fatal “skip and continue” condition.

For example:

```python
try:
    response = input("Would you like to configure them now? [Y/n]: ").strip().lower()
except EOFError:
    response = "n"
except UnicodeDecodeError:
    print("  ℹ Unreadable terminal input — skipping config migration prompt.")
    print("    Run 'hermes config migrate' later to apply any new config/env options.")
    response = "n"
```