REPO_POLICIES: fix the second review's findings on the compaction (#158)

Fixes the seven findings of
#159 (comment), with
the wording each one gives.

- Go key points: "whatever files the mount holds".
- `.dockerignore`: "Such a `.dockerignore` is more dangerous than a
  short file with no secret patterns at all".
- Python: "pipenv checked the hashes of the lockfile's packages".
- Python: "In that step" leads only the two bullets about that step.
  The other four sit under "A Python repository's `script/bootstrap`:".
- Entrypoints: "Three more scripts have no required target:".
- Dockerfile: the two ways a stage installs what its image lacks are
  bulleted again, as on `next`.
- Version: the sentence ends at "stage-scoped", then "It has no
  default."
- `TODO.md`: the entry carries the new size, 1,066 lines and 7,812
  words.

Model: fable-5-1

TODO.md

@@ -27,7 +27,7 @@ fmt-check, and commit.
   pins `golines`. The Go style guide and both checklists say the same. `lll`
   stays at 88, since `golines` leaves long strings and comments as they are.
 - 2026-11-06: Compacted `prompts/REPO_POLICIES.md` from 1,145 lines and 8,427
-  words to 1,062 lines and 7,794 words
+  words to 1,066 lines and 7,812 words
   (https://git.eeqj.de/sneak/prompts/issues/158). Every rule keeps its meaning.
   The rules now sit under headings, the pinning rule first. Each rule that was
   stated in several places is stated once. The Makefile copies of the Go and