Re-vendor the shared files from sneak/prompts at dd4027b (closes #504)

The shared workflow, lint config, prettier settings and policies are the copies at `sneak/prompts` commit `dd4027b`. `.gitignore`, `.editorconfig` and `.dockerignore` are the shared copy followed by this repository's own entries. Linting is the image build's lint phase on golangci-lint v2.14.0, and tests run in their own test phase. Every scripted `docker build` passes `--no-cache`, so the CI fingerprint step and the superseded-run script are gone. The binary is built with `-trimpath -s -w`, and a build that has `.git` but no version fails. The development run keeps its databases outside the checkout.

Deviation: `.dockerignore` also leaves out SQLite databases at any depth.

Model: opus-5-5

script/bootstrap

@@ -60,10 +60,10 @@ main() {
     if missing go; then pkg_install go golang go go; fi
 
     # Not installed here: docker is platform-specific and out of scope for a
-    # package-manager bootstrap, but script/lint, script/fmt and script/css
-    # need it.
+    # package-manager bootstrap, but script/test, script/lint, script/fmt and
+    # script/css need it.
     if missing docker; then
-        echo "bootstrap: docker not found; script/lint, script/fmt and script/css require it" >&2
+        echo "bootstrap: docker not found; script/test, script/lint, script/fmt and script/css require it" >&2
     fi
 
     go mod download