rename the project to khosra, initialise the module

Naming is free before a module is published, a URL is shared, or a binary is
deployed; every day it waits costs more. Swept every form: module path, binary,
cmd/ directory, KHOSRA_SITE, the feature-loop skill directory, and the prose in
earlier ADRs — which describe this project under its old name, not a different
project. Recorded as ADR-0030.

go mod init lands here rather than with the first feature because the module
path is what the rename is about. x/text and yaml.v3 are required but not yet
imported, so both are indirect and no direct dependency is claimed yet.

docs/extensions.md

@@ -41,7 +41,7 @@ type Extension struct {
 }
 ```
 
-`cmd/atelier/wire.go` holds the only list of enabled extensions. Enabling or disabling one is a
+`cmd/khosra/wire.go` holds the only list of enabled extensions. Enabling or disabling one is a
 one-line diff and a rebuild. Removing one leaves no trace elsewhere — that property is the test of
 whether the contract is right.