fix(mcp-suite): fail closed on unreadable hook context

[djm204]

Summary

• Treat a configured but unreadable FBEAST_TOOL_CONTEXT_FILE as a hard hook failure
• Prevent pre-tool governance from falling back to empty or legacy positional context
• Add a regression proving the governor is never called when context acquisition fails

Verification

• npm run test --workspace @franken/mcp-suite (614 passed)
• npm run typecheck --workspace @franken/mcp-suite
• npm run lint --workspace @franken/mcp-suite (0 errors; 26 pre-existing warnings)
• npm run build
• node scripts/check-hardcoded-secrets.mjs

Closes #3665

[djm204]

@codex review

[chatgpt-codex-connector]

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[djm204]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Breezy!

Reviewed commit: 0e2b546d2f

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