docs: open each module's readme with its install, a framework example and a prompt for an assistant - #67

GitHub Packages shows no README for a Maven package, only a Maven snippet and "No description available yet", so a reader landing there or in a module folder had to go to .docs/install.md for the dependency line and to .docs/usage.md for a first call.

Each module's README now opens with:

• Install: the Gradle (Kotlin DSL) line for that artifact, Maven collapsed under it, sbt first for Play, and a pointer to .docs/install.md for the repository block and the token;
• Configure: what was already there, followed by a Payments bean in that framework's idiom (@Service, jakarta.inject.Singleton, @ApplicationScoped, Play's javax.inject), with its imports, reading the money received and booked over the last week through moneta.with(token); Kotlin collapsed beside Java, except for Play. Under it: what happens with several accounts or without the token property.

For a coding assistant: llms.txt at the root (the setup and the mistakes to avoid, linked from the README), and a prompt to paste in each module's README, naming that module's artifact, configuration and README, written for no tool in particular.

Play's pool example now calls that bean instead of moneta.incoming(…) with undefined arguments. modules/moneta-api/README.md is new, the same for the plain client. Beside the new text: "merchants" became "account holders", the long dash in the property tables "none".

.docs/install.md names 0.2.0, and make publish-local now installs 0.3.0-SNAPSHOT instead of 0.1.0-SNAPSHOT, which sorted below the released version.

The version is written in five more places; make release does not bump them, so each release edits them by hand until it does.