ecore: the gaps the third adoption pass found

Five services adopted the new packages today and each hit the same edges.

bearer.IsRefusal: a service's resolver returns more than this package's
vocabulary — the Postgres lookup it had to make, an expired context, a bug —
and StatusFor's default answers those 401, which tells a caller to re-mint a
token that was never the problem. Every service that wrapped the table spelled
out the sentinel list to guard the delegation; now it does not have to.

instconf.Key.Because: three services kept their own hand-written config
checker rather than lose the sentence that says WHY a key is required
("crypto.InitCrypto exits without it"). Require reported the names and nothing
an operator could act on, so nobody used it.

logging.DefaultsWithoutDebugFlag: a migration CLI passes -d to brant, where it
means --dialect and takes a value, so `coversrht-migrate -d postgres` arrived
as a request for debug logging — silently, because the probe sees the flag and
never the value.

assets.DirFS: os.DirFS("") does not mean "no assets", it means "serve the
filesystem root", and it is one unset config key away. dolt wrote the guard;
the other five would each have to see it happen first.

pages.APIMessage: the REST half of every service keeps its 404 body
byte-identical on purpose, so it could not adopt the shared refusal installer,
whose messages are page sentences. The same table now answers in both
registers.

bearer, pages: the refusal table and the form read that must not drift

bench wrote the bearer refusal switch three times in one repo — REST, MCP and
its resolver — and each copy re-decides the arm that matters: ErrUnavailable
is 503, never 401. Reading an unreachable token daemon as "revoked" tells
every CI job on the instance its credential is bad for as long as tokens.sr.ht
takes to restart. That warning has lived in this repo's README as prose, where
it cannot be imported; StatusFor puts it in code, and its default sends an
unrecognised failure to 401 so a forgotten arm refuses a request rather than
declaring the service unwell.

FormValues returns r.PostForm and never r.Form. r.Form merges the query string
into the body's values, so a mutation could be driven from a URL somebody was
linked to — the one request the same-origin guard cannot fault, because it did
come from our own page. The difference between the safe version and the hole
is one character in a field name, in a function every service with a form
writes for itself.