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 Every scripted `docker build` passes `--no-cache`, so the CI fingerprint step and the superseded-run script are gone.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/css

@@ -2,14 +2,16 @@
 # script/css: regenerate static/css/tailwind.css (writes). tailwindcss is
 # never installed locally: it runs in docker, at the version and sha256
 # pinned in the Dockerfile's stylesheet stages, which also say what the
-# stylesheet is generated from.
+# stylesheet is generated from. --no-cache, as on every docker build in
+# script/, so the stylesheet is generated rather than taken from the cache.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    docker build --target css-output --output type=local,dest=static/css .
+    docker build --no-cache \
+        --target css-output --output type=local,dest=static/css .
 }
 
 main "$@"