fix(sourcehunt): bound deep searches and stall decisions

[jorge-garcia-le]

Summary

• Add bounded repository content and path searches to deep hunters, with explicit empty and truncated results.
• Guide hunters from search hits to source reads, block shell grep/find searches, and limit search-only stall resets while preserving the eight-step guard.
• Require a final evidence-based decision for an active potential at the stall boundary.

Verification

• uv run --group dev pytest -q tests/test_deep_agent_loop.py tests/test_deep_agent_tools.py tests/test_sourcehunt_subsystem.py tests/test_unconstrained_prompt.py — 137 passed.
• Ruff lint and format checks pass for all changed Python files; git diff --check passes.
• Repository-wide pytest -q — 3,769 passed, 1 skipped, 3 failed in test_machine_cli.py, test_minimax_compat.py, and test_otel.py (outside the changed files).
• Repository-wide Ruff checks report existing issues in untouched files.