test(discovery): install the three no-installer families

[pengyuzhang]

Stacked on #69.

A recipe installs, verifies and locates in a single call, because the three are inseparable: one that installed without verifying would let the runner record a version it never saw, and the scorer would then compare the collector against the manifest's intention rather than against the disk.

Three families, chosen deliberately

family	entries	needs
declare-mcp	27	a JSON/TOML/YAML writer
artifact	24	file and symlink writes
npm-global	9	one command

Between them, 60 of Linux's 105 entries with no vendor installer, no GUI session, no network beyond a registry and no model downloads. They are also the two categories where the collector does the most inference, so the cheapest half of the manifest exercises the most interesting logic.

The other eleven record unimplemented

A deliberate fourth status beside installed / unavailable / failed. It keeps those entries out of the denominator and keeps them loud — a harness that silently omitted them would report a recall computed over whatever happened to work.

Each names the phase it belongs to rather than inheriting a default stub, so adding a family to the manifest without a recipe fails loudly instead of quietly no-op'ing.

The same status covers an entry whose vendor source is unresolved. A URL nobody has filled in is a harness gap, and must never be reported as a vendor that stopped shipping.

Every recipe verifies what it created

This came from a live run, not from review. On the first pass against an Ubuntu guest, N-09's symlink was silently absent and recorded installed — the transport could not write to /usr/local/bin and nothing checked.

That is the worst failure available to this harness, because it manufactures a defect in the thing it measures: the scorer would have reported the collector missing a file that was never there. Both implemented file-writing recipes now check afterwards and record failed with the real reason.

Verification

$ python3 -m unittest discover -s tests -t . -q
Ran 86 tests in 0.046s
OK

implemented: ['artifact', 'declare-mcp', 'npm-global']
pending:     11 families
every family resolves to a recipe or a stated gap: True

The live results these recipes produced are in the runner PR that follows.