fix: count published pages, not index.html files

[toastygm]

package-build 15 (HeroicLands/package-build#182) gave a package's landing an
address of its own, /<package>/homepage-<shortcode>/, and Hugo went on
generating a site root at /<package>/ beside it — chrome around an empty
<main> that nothing in the toolchain writes and _redirects sends visitors
past. The guard counts index.html files, so that root read as a second page
and failed kethira on every push from the day it took package-build 15.

Discount the package-root index.html from the tally, in both modes, so "a
page" means one thing in this file. Discount it only when the addressed landing
is present beside it, matched as homepage-*: three callers still build the
pre-#182 shape, where that file IS the landing and subtracting it would tally
zero and fail all three at once. Keying on the landing rather than on "more than
one file" also keeps the licensing bound intact in both shapes — a homepage-only
package that published one real extra page tallies two either way.

The separate assertion that the deployment root exists and is non-empty stays;
it is a different check, and its comment no longer calls that file the home page.

Confirmed page inventory — clean origin/main builds of every caller, on
this machine:

package	package-build	index.html files	tally after the fix
kethira	15	homepage-root/index.html (7,419 B, 1,294 visible chars in <main>) + index.html (4,916 B, 0 visible chars in <main>)	1
harnadventures	9	index.html — the landing itself	1
harnensemble	10	index.html — the landing itself	1
hm3	9	index.html — the landing itself	1

content-build site reports wrote 1 homepage(s) + 0 content page(s) + 0 tree page(s) + 0 landing(s) for kethira. The content side was never wrong.

Verification. The guard's run: body was extracted verbatim and driven
against the four real build trees and a set of constructed ones:

tree	mode	expected	result
kethira, as built	homepage	pass	pass — 2 index.html file(s); 1 page(s)
harnadventures / harnensemble / hm3, as built	homepage	pass	pass — 1 page(s)
kethira + a genuinely built second content page at /kethira/deity-agrik/	homepage	reject	rejected — 2 page(s)
harnadventures (pre-#182 shape) + a second content page	homepage	reject	rejected — 2 page(s)
content tree, new shape, 1,714 pages, min-pages: 1000	content	pass	pass
content tree collapsed to Hugo's root alone	content	reject	rejected
content tree collapsed to the landing alone	content	reject	rejected
nothing at all	homepage	reject	rejected at the root check

shellcheck is clean on the extracted body and the file parses as YAML.

Effect on callers. All four callers of this workflow are
publish.site: homepage and none passes min-pages/max-pages (homepage mode
rejects them). sohl and sohl-thalorna do not call this workflow — each still
deploys from its own hand-written one, and thalorna's floor (test "$pages" -gt 1000) lives in that file and is untouched by this change. So no declared
threshold moves anywhere, which is also why discounting in content mode costs
nothing today.

Closes #20