Warn on SDK config load failures

[d42me]

Adds warning logs when SDK config files cannot be parsed/read across MCP, evals, sandboxes, and tunnel packages, with a caplog regression test.

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Note

Low Risk
Low risk: only adds warning logs and slightly broadens exception handling when reading local config files; no behavior change beyond improved visibility and consistent fallback.

Overview
Adds warning logs across the various SDK Config loaders (evals, MCP server, sandboxes, tunnel) when ~/.prime/config.json cannot be read or parsed, and standardizes the failure path to fall back to an empty config (catching OSError instead of IOError).

Introduces a regression test (test_sdk_config_load_warnings.py) that parametrically verifies each package emits the warning and returns {} when the config file contains invalid JSON.

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