Fix Sigil CLI import on Python 3.12+

[sedge-bot]

Summary

• Avoid nested f-string quoting that breaks on Python 3.12+ when importing the Sigil CLI.
• Keeps the CLI importable and the demo status command working.

Verification

• python3 -m py_compile tools/intent/sigil.py
• python3 tools/intent/sigil.py --help
• python3 tools/intent/sigil.py status --repo examples/demo-app
• git diff --check github/main...HEAD

Workspace tracker: SEDGE-433b3f

[sedge-bot]

Heartbeat verification pass for this PR head (61e81ae):\n\n- uv run --with pytest pytest -q tools/intent/tests/test_show.py tools/intent/tests/test_graph.py → 19 passed\n- python3 -m py_compile tools/intent/sigil.py → passed\n- git diff --check github/main...HEAD → passed\n\nGitHub reports the PR as MERGEABLE/UNSTABLE, but there are no status checks attached in statusCheckRollup; this local verification covers the touched CLI show/graph path.

[sedge-bot]

Heartbeat verification pass for this PR head (61e81ae):

• uv run --python 3.12 --with pyyaml python - <<'PY' ... py_compile + runpy ... PY -> passed on CPython 3.12.13; main is callable after import.
• uv run --with pytest pytest -q tools/intent/tests/test_show.py tools/intent/tests/test_graph.py -> 19 passed.
• python3 -m py_compile tools/intent/sigil.py -> passed on Python 3.11.2.
• git diff --check github/main..HEAD -> passed.

I also started the full pytest suite with uv run --with pytest pytest -q; it progressed past the first 103 tests but exceeded the 10-minute heartbeat budget, so I am not claiming a full-suite pass. GitHub still reports the PR as MERGEABLE/UNSTABLE with no status checks in statusCheckRollup; the Python 3.12 import/compile smoke directly covers the PR's f-string import fix.