fix(mcp): tolerate malformed client env

[yyswhsccc]

Problem

rustchain-bounties-mcp/rustchain_bounties_mcp/client.py parsed RUSTCHAIN_TIMEOUT and RUSTCHAIN_RETRY directly at import time. A malformed local environment value raises ValueError before the MCP client can start.

Impact

A single bad numeric env value can crash the RustChain bounties MCP client during startup, preventing bounty/node tooling from initializing until the environment is corrected.

Fix

Add a small local _safe_int_env helper that logs malformed numeric env values and falls back to the existing defaults. Valid numeric env overrides are preserved.

Tests

• uv run --no-project --with pytest --with pytest-asyncio --with aiohttp python -B -m pytest -q tests/test_client_miners.py -> 4 passed
• python3 -m py_compile rustchain_bounties_mcp/client.py tests/test_client_miners.py -> passed
• git diff --check -> passed

Boundaries

Related to the general bug bounty surface (#305). This PR does not change payout amounts, wallet crediting, admin secrets, or production wallet behavior.

wallet: RTC47bc28896a1a4bf240d1fd780f4559b242bcd945

[yyswhsccc]

@Scottcjn Please take a look when you have a chance. This is a small MCP client startup hardening fix: malformed RUSTCHAIN_TIMEOUT / RUSTCHAIN_RETRY values now fall back to existing defaults instead of crashing import/startup.

Validation:

• uv run --no-project --with pytest --with pytest-asyncio --with aiohttp python -B -m pytest -q tests/test_client_miners.py -> 4 passed
• python3 -m py_compile rustchain_bounties_mcp/client.py tests/test_client_miners.py -> passed
• git diff --check -> passed

[jaxint]

✅ Code reviewed - implementation verified.

[jaxint]

✅ Code reviewed - implementation verified. Good work on the changes.

[jaxint]

Nice implementation! This is a valuable contribution.

Reviewed for Bounty #71
Wallet: AhqbFaPBPLMMiaLDzA9WhQcyvv4hMxiteLhPk3NhG1iG