CLI self-description still says "clonable template" — contradicts every harness prompt

[OriNachum]

The four harness prompt files and the README now describe this repo as an
agent-first CLI for managing a Substack publication (currently a scaffold) —
see #2. The CLI's own self-description still says "clonable template for
AgentCulture mesh agents", so substack learn and substack --help tell an
agent something every prompt file contradicts.

Surfaced by an ask-colleague review on #2 as "the single most visible
remaining drift". Deliberately left out of #2, which was doc-only.

Locations

substack_cli/cli/__init__.py:74      parser description
substack_cli/cli/_commands/learn.py:15, :21   learn text ("Clone it, rename the package…")
substack_cli/cli/_commands/learn.py           _as_json_payload()["purpose"]
substack_cli/explain/catalog.py:15, :18, :84  root entry + overview entry
substack_cli/cli/_commands/whoami.py:7        docstring ("When you clone this template…")
substack_cli/cli/_commands/overview.py:4      docstring + _ARTIFACTS / _VERBS wording
substack_cli/cli/_commands/doctor.py:7, :40   docstring ("this template")

overview.py's _ARTIFACTS also names culture.yaml + AGENTS.colleague.md as
the mesh identity pair, which is wrong for this repo — culture.yaml declares
backend: claude, so the resident prompt is CLAUDE.md.

Constraints

• learn must keep covering purpose, command map, exit codes, --json, and
  explain, and stay >=200 chars — teken cli doctor . --strict checks it.
• tests/test_cli.py and tests/test_cli_introspection.py assert on some of
  this output; update them in the same change.
• Keep the scaffold honesty the docs now carry: the description should say what
  the CLI is for without implying the post/subscriber/stats verbs exist yet.

Related

The substack (binary) vs substack-cli (dist name, argparse prog) mismatch
is a separate decision, also documented in #2 but not fixed there. Worth
settling in the same pass since both touch the same strings.