docs: inconsistent guidance on Call value (examples say value=0, but docs use value=1000)

[devorun]

Describe the change

The docs give contradictory guidance on the value field of Call, aimed at end-users following the examples.

examples/README.md states native value transfers are unsupported and examples must use value=0:

Tempo doesn't support native transfers (sending ETH value), so transactions use value=0

and both runnable examples (examples/simple_send.py, examples/batch_calls.py) use value=0.

However, nearly every other example in the docs uses a non-zero value (value=1000):

• docs/getting-started.md, docs/index.md, README.md
• all of docs/guides/*.md
• the docstrings in pytempo/__init__.py and pytempo/models.py

At the SDK level, Call only validates value >= 0 (pytempo/models.py), and some tests exercise non-zero values (e.g. tests/test_integration.py, tests/test_keychain.py).

Could you confirm the intended behavior so the docs can be made consistent?

1. If the chain ignores/rejects native value transfers, then the getting-started and guides examples using value=1000 are misleading and should use value=0.
2. If a non-zero value is valid, then the note in examples/README.md should be corrected or removed.

Happy to open a follow-up PR to align the docs once the intended behavior is confirmed.

Additional context

Same-file network reference fix is already in #73. This issue tracks the separate value guidance inconsistency.