analyze: run condor compute jobs via .venv/bin/giant, not uv run

uv isn't installed on the HTCondor worker docker image, so `uv run`
fails there. giant is already an installed console script in the
repo's uv-synced .venv, so exec it directly instead. write_submit now
fails fast with a clear message if .venv/bin/giant is missing.

giant/analysis/condor.py

@@ -316,7 +316,7 @@ class SubmitConfig:
 _WRAPPER = """#!/bin/bash
 set -euo pipefail
 cd {repo_dir}
-exec uv run giant analyze compute-one --id "$1" --chunk "$2" --run-dir {run_dir}
+exec {repo_dir}/.venv/bin/giant analyze compute-one --id "$1" --chunk "$2" --run-dir {run_dir}
 """
 
 
@@ -375,6 +375,14 @@ def write_submit(cfg: SubmitConfig, ids: list[str] | None = None) -> Path:
     Returns the submit description path (``<run_dir>/analyze.sub``). Does not
     submit — call ``condor_submit`` on the returned file.
     """
+    venv_giant = cfg.repo_dir / ".venv" / "bin" / "giant"
+    if not venv_giant.exists():
+        raise FileNotFoundError(
+            f"{venv_giant} not found — condor jobs run it directly (no `uv` on "
+            f"the worker image), so run `uv sync --extra cpu` in {cfg.repo_dir} "
+            "before submitting."
+        )
+
     ids = ids or catalog_ids()
     run_dir = cfg.run_dir
     (run_dir / "logs").mkdir(parents=True, exist_ok=True)