* chore(installer): remove dead code across installer modules
Delete 3 entirely dead files (agent-command-generator, bmad-artifacts,
module-injections) and remove ~50 unused exports from manifest.js,
cli-utils.js, prompts.js, path-utils.js, official-modules.js,
external-manager.js, custom-module-manager.js, and registry-client.js.
Removes corresponding dead tests.
* fix(installer): restore currentProjectDir writes for placeholder expansion
The previous commit removed the three assignments to
OfficialModules.currentProjectDir as dead code, but buildQuestion()
still reads the property to resolve {directory_name} placeholders in
module config defaults during interactive collection. Without the
writes, any module default containing {directory_name} would surface
the literal placeholder to users.
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