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 Every scripted `docker build` passes `--no-cache`, so the CI fingerprint step and the superseded-run script are gone.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

Makefile

@@ -19,6 +19,10 @@ override VERSION := $(or $(strip $(VERSION)),$(shell script/version))
 # Extra linker flags for the build target. The static relink in the
 # Dockerfile adds -extldflags here rather than passing its own -ldflags,
 # so composing flags cannot drop the version stamp.
+#
+# The build target itself always passes -trimpath and -s -w, as the Go
+# Dockerfile in REPO_POLICIES.md does: no build paths, symbol table or
+# debug information in the binary.
 GO_LDFLAGS ?=
 
 bootstrap:
@@ -49,7 +53,7 @@ check:
 	@script/check
 
 build: assets
-	go build -ldflags '$(strip -X main.version=$(VERSION) $(GO_LDFLAGS))' -o bin/webhooker ./cmd/webhooker
+	go build -trimpath -ldflags '$(strip -s -w -X main.version=$(VERSION) $(GO_LDFLAGS))' -o bin/webhooker ./cmd/webhooker
 
 run: build
 	./bin/webhooker