Format Markdown with prettier and move documents out of the root (closes #411)

REPO_POLICIES.md names prettier as the Markdown formatter and keeps documents out of the root. script/fmt and script/fmt-check now run prettier over all Markdown (4-space indents, proseWrap always) besides gofmt, with node and yarn installed by script/bootstrap as in sneak/prompts. All Markdown is reformatted with no text change. ARCHITECTURE.md and TODO.md move to docs/, config.example.yml to configs/, and every reference follows.

Model: opus-5-5

internal/config/config_test.go

@@ -90,12 +90,12 @@ func TestConfigLoad(t *testing.T) {
 }
 
 // TestExampleConfigIsScrubbedAndLoads checks that the shipped
-// config.example.yml carries only neutral placeholders (no real credentials,
-// private addresses, or internal host names) and still parses.
+// configs/config.example.yml carries only neutral placeholders (no real
+// credentials, private addresses, or internal host names) and still parses.
 func TestExampleConfigIsScrubbedAndLoads(t *testing.T) {
 	t.Parallel()
 
-	examplePath := filepath.Join("..", "..", "config.example.yml")
+	examplePath := filepath.Join("..", "..", "configs", "config.example.yml")
 
 	cfg, err := Load(examplePath)
 	if err != nil {
@@ -361,7 +361,7 @@ func TestDocumentedSizeDefaults(t *testing.T) {
 }
 
 // TestDocumentedSizeExamples checks the 1MB minimum chunk_size and that
-// every size the README, config.example.yml and the config init template
+// every size the README, configs/config.example.yml and the config init template
 // list as an example is accepted.
 func TestDocumentedSizeExamples(t *testing.T) {
 	t.Parallel()