fix(deliberation): stop passing --markdown/--limit to graph probe commands

[solomonneas]

What

The deliberation scope planner appended --markdown --limit 8 to every graphtrail call, but only context accepts those flags. callers, callees, and impact reject them and exit non-zero, so the planner always derived a single evidence scope and rejected every --deliberate plan before dispatch.

This is the direct cause of route C's 0/10 in the #442 experiment: 8/8 cases failed pre-dispatch with deliberation could not assemble enough grounded GraphTrail evidence scopes and route C never made a model call.

Change

• _graphtrail_markdown is now _graphtrail_scope_text and only passes --markdown --limit 8 on the context probe.
• Regression test with a fake graphtrail binary that mirrors the installed CLI's flag surface (rejects --markdown/--limit on the three probe commands). The existing tests mocked derive_evidence_scopes wholesale, which is why this was never caught.

Verify

./scripts/verify passed locally (Brigade verify run 20260724-010851-work-verify-e2ec06, exit 0). The new test fails on main and passes here.

Notes for review

This fixes the mode's entry path; it takes no position on whether the flag stays. That call is tracked in #442 and the experiment scoring there was produced with the mode broken, so route C remains unmeasured until a rerun.

Refs #442

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