`wvr module new` scaffold, module authoring guide, and self-describing manifest

[Max-Levitskiy]

Priority: P2 · Epic: #82 · Refs: marketplace design G7, spec 004 US-6

What

1. wvr module new <name> [--dir <path>] [--profiles a,b] writes:

   weaver.module.yaml        # inputs, one example rule per face type, profiles comment
   templates/README.md.j2
   sections/example.md.j2    # for text.section rules
   tests/cases/basic/{before,after,weaver.yaml}   # for #84
   .wt/weaver/manifest.yaml  # discovery metadata (marketplace design §A)
   README.md                 # adoption steps for consumers
   

2. docs/MODULE_AUTHORING.md: the engine-accurate model (what is templated and what is
   not, module-relative paths, path: subdirectories, how rules map to plugin types,
   profiles/when:/waivers, versioning with tags, how a consumer pins), replacing the
   folklore currently spread across beads-module-handoff.md §2.
3. wvr module validate [<dir>]: parses the manifest, checks every rule type resolves
   to a plugin (declared or bundled), every content_from_template/template path
   exists, ids are unique, profiles referenced by when: are declared.

Acceptance

• Scaffolded module passes wvr module validate and wvr module test out of the box.
• The guide is used to author the dev-standards module without reading engine source
  (feedback loop: gaps found there become follow-up issues).

Depends on

#75, #76, #74.