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 Every scripted `docker build` passes `--no-cache`, so the CI fingerprint step and the superseded-run script are gone.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

internal/middleware/loginguard_test.go

@@ -236,9 +236,9 @@ func TestLoginGuard_SemaphoreBoundsConcurrentVerifications(
 
 		// rendezvousDeadlock is the deadlock guard described below.
 		// It is orders of magnitude longer than any scheduling delay,
-		// so it never decides the result, and well inside script/test's
-		// 30s timeout, so a wedge fails on the assertion instead of
-		// blowing the package timeout.
+		// so it never decides the result, and well inside the 90s
+		// package timeout of the Dockerfile's test phase, so a wedge
+		// fails on the assertion instead of blowing that timeout.
 		rendezvousDeadlock = 5 * time.Second
 	)