fix(hooks): parse Stryker commands instead of scanning for the tool name

[bdfinst]

Summary

• Both C# mutation PreToolUse gates (mutation_testing_smoke_gate.py, stryker_xunit_shim_guard.py) decided "is this a Stryker run?" with a bare re.search over the whole command string — any command merely mentioning the tool name in prose (a --body, a grep, an echo, a Python comment) was treated as an invocation and blocked.
• Extracted a shared hooks/lib/stryker_invocation.py::is_stryker_invocation() predicate: tokenize with shlex (punctuation_chars mode, so &&/||/;/| are recognised as their own tokens while quoted text stays one token), split into operator-separated segments, and match the tool only in program position of a segment. Heredoc bodies are stripped before tokenizing. Falls back to the old permissive regex only when shlex can't tokenize the command at all, so a malformed command still fails closed.
• Both gates now delegate to the shared predicate instead of keeping their own drifting copy, with the old regex kept only as each hook's degraded-import fallback (hooks/lib unreachable).

Test Plan

• TDD-first per the issue: added the four false-positive repro cases as tests against today's implementation first, confirmed 3/4 failed outright and the 4th silently passed for the wrong reason (coincidental -t mtp match) — proving the bug — before writing the fix.
• python3 -m pytest plugins/dev-team/tests/hooks/test_stryker_invocation.py plugins/dev-team/tests/hooks/test_mutation_testing_smoke_gate.py plugins/dev-team/tests/hooks/test_stryker_xunit_shim_guard.py -q — 106 passed, including all pre-existing trigger cases (cd <dir> && dotnet stryker ..., dotnet-stryker, the wrapper script) unchanged
• python3 plugins/dev-team/skills/code-review/scripts/repo_invariants.py and internal_double_detector.py static pre-passes — clean
• python3 scripts/check_md_references.py — clean
• Full pre-PR pytest gate (plugins/dev-team/tests tests/repo tests/agents tests/commands tests/docs tests/knowledge tests/stack_aware tests/skills tests/scripts tests/hooks) — 10786 passed, 48 skipped
• pre-push hook's own local CI — all checks passed

Closes #2185

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https://claude.ai/code/session_016uBnw1i52qEik2k9LSHa4n

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