Say where a repository's own .gitignore and .editorconfig entries go (closes #103)

The canonical `.gitignore` and `.editorconfig` now each end with a comment saying a repository's own entries go below it and a re-vendor keeps them, as `.dockerignore`'s header already does; without it a re-vendor dropped a repository's binaries and test outputs from `.gitignore`. `.editorconfig` gains `[*.go]` with tabs, since `gofmt` decides Go indentation in every repository. `prompts/REPO_POLICIES.md`, both checklists and the Go styleguide say the same in plain sentences. Common outputs such as `*.test` stay out of the canonical `.gitignore`. This also covers #104.

Model: opus-5-5

prompts/NEW_REPO_CHECKLIST.md

@@ -1,6 +1,6 @@
 ---
 title: New Repo Checklist
-last_modified: 2026-10-04
+last_modified: 2026-10-06
 ---
 
 Use this checklist when creating a new repository from scratch. Follow the steps
@@ -34,14 +34,17 @@ Template files can be fetched from:
 ## Fetch Template Files
 
 - [ ] `.gitignore` — fetch from
-      `https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitignore`, extend for
-      language-specific artifacts. Extensions are written to `.gitignore`'s own
-      semantics, where an unanchored pattern already matches at every depth:
-      never add a `**/` prefix here, which is a `.dockerignore` form. The
-      canonical file already carries `.claude/` so agent worktrees cannot be
-      committed by accident.
+      `https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitignore`, then add
+      the repo's own build outputs, such as its binaries, at the end of the
+      file, where a re-vendor keeps them. Extensions are written to
+      `.gitignore`'s own semantics, where an unanchored pattern already matches
+      at every depth: never add a `**/` prefix here, which is a `.dockerignore`
+      form. The canonical file already carries `.claude/` so agent worktrees
+      cannot be committed by accident.
 - [ ] `.editorconfig` — fetch from
-      `https://git.eeqj.de/sneak/prompts/raw/branch/main/.editorconfig`
+      `https://git.eeqj.de/sneak/prompts/raw/branch/main/.editorconfig`, then
+      add the repo's own sections, such as one for another language it uses, at
+      the end of the file, where a re-vendor keeps them.
 - [ ] `Makefile` — fetch from
       `https://git.eeqj.de/sneak/prompts/raw/branch/main/Makefile`, adapt
       targets for the project's language and tools