fix: conformance tool Windows crash + remove redundant mediaType from local-business example

[hammer-build]

What this fixes

Two independent issues found while running the conformance tool against the new example catalogs on Windows.

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1. Conformance tool crashes on Windows (conformance/bin/conformance-test)

Problem: The tool uses ✓, ✗, and ⚠ for output. Windows terminals default to cp1252 encoding which cannot encode these characters — the tool crashes immediately before validating anything, printing a UnicodeEncodeError traceback.

Fix: Reconfigure stdout/stderr to UTF-8 at startup:

if hasattr(sys.stdout, 'reconfigure'):
    sys.stdout.reconfigure(encoding='utf-8', errors='replace')
    sys.stderr.reconfigure(encoding='utf-8', errors='replace')

reconfigure is available from Python 3.7+. The call is a no-op on terminals already in UTF-8 mode (Linux, macOS), so cross-platform behaviour is unchanged.

2. Redundant mediaType field in local-business example

Problem: Both entries in local-business-catalog.json have a top-level mediaType field that duplicates type:

"type": "application/a2a-agent-card+json",
"mediaType": "application/a2a-agent-card+json"

mediaType at entry level is not part of the ARD spec — type already carries the IANA media type. It is absent from all other catalog examples (basic, fda-ndc, noaa-weather). As a teaching example, having an extra non-spec field risks confusing readers.

Fix: Remove both occurrences. All conformance checks still pass.

Testing: Verified on Windows (Python 3.13, cp1252 terminal) without setting PYTHONIOENCODING:

python conformance/bin/conformance-test manifest conformance/examples/local-business/local-business-catalog.json
→ CONFORMANCE STATUS: PASS  (exit 0)