fix(templates): guard the release zip; correct stale architecture docs

[akshat009]

What

Three areas, all landing in every scaffolded plugin (plus the CLI's own README).

1. The release zip can no longer be built broken

templates/package.json:

• plugin-zip chains composer prepare-dist — "composer prepare-dist && wp-scripts plugin-zip". Previously npm run plugin-zip with no vendor/ on disk produced a zip with no autoloader, exit 0, no warning.
• assets/src/ removed from files[] — verified nothing in generated runtime PHP reads it (Block_Registrar → assets/build/blocks, Woo integration → assets/build/blocks-integration.js, Interactivity → assets/js/view.js; every assets/src mention is a doc comment).
• templates/readme.txt gains a == Development == section pointing to the repo for unminified source — gated on has_webpack_build, links {{AUTHOR_URI}} when set, else a fill-in placeholder. Keeps the wp.org "human-readable code" requirement satisfied now that source isn't shipped.

2. Stale architecture docs

Both templates/README.md and the CLI's own README.md described a Plugin::create() / Core\Container / Contracts\Service_Provider / Contracts\Conditional / <prefix>_providers filter system the generator has never produced. The real design is a singleton Plugin::instance()->boot() running a flat list of ( new X() )->init_hooks() calls.

• templates/README.md: the section is replaced with a plain, module-aware ## Project structure list (conditional assets/src/ and templates/ lines) — a generated plugin's README shouldn't carry an architecture essay.
• README.md (CLI): ## Architecture (generated plugin) rewritten to match the code; intro line and module-table wording corrected; Releasing sections updated for the chained plugin-zip.

3. Supporting

• index.js: new has_author_uri template flag; Next steps output now points at the Releasing section.
• tests/generator.test.js: updated the two plugin-zip string assertions and the files[] assertion (now asserts assets/src is absent).

Not included

No version bump — following repo convention (bumps are separate release commits). Next release should be a minor (3.0.0 → 3.1.0): plugin-zip now requires Composer on PATH and generated output changes, but the CLI interface is unchanged.

Verification

• node --test tests/*.test.js → 70/70 pass
• Regenerated scaffolds across build/no-build and woo/no-woo: readme.txt, README.md, package.json render with no stray {{...}} tokens; ## Project structure matches the actual directory tree in each combo
• Full real pipeline exercised end-to-end (npm run build → composer install --no-dev --optimize-autoloader → npm run plugin-zip): 68-file zip, vendor/ present with a clean autoloader (no phpunit/phpcs/wpcs leak), deployed and structurally validated