chrome: a default favicon, optional listing columns, and a table partial

Three services asked for a favicon field and bench argued against one: it
ships no icon deliberately, and its layout says why — a <link rel="icon">
pointing at an asset the binary does not have is a 404 on every page load, for
a file nobody asked for. A default that is a path hands that to every service
without a logo, so the default carries its own bytes instead: the brand's ring
as a data: URI, which cannot 404 and costs no request. It is a template.URL
because html/template rewrites any href whose scheme is not http, https or
mailto to "#ZgotmplZ" — the type is how a caller says it meant a data: URI.

Updated and Meta are optional for the reason the four listing services could
not agree: bench and spec have a modification time, dolt's schema has no
timestamp at all, and cover's index is a table of sparklines no shared partial
will render. A required column would have pushed dolt back onto a local copy.
Updated is a time.Time so the partial renders "3 hours ago" with the exact
stamp in the title once, rather than five services spelling it five ways.

srht-repo-table is a second partial over the same dot rather than a variadic
first one: growing columns on the cards would have made them worse cards for
the services that wanted cards.

Attach now installs Funcs itself, because the partials call reltime and
abstime and an unknown function is a parse error — a caller who had not merged
Funcs would have got a startup panic naming a template it never wrote. pages
consequently attaches before layering the service's own map on top, which is
what keeps a deliberate shadow working.

chrome: shared page chrome for the instance's custom services

Extract the nav/chrome idiom that compare, spec, dolt and cover each
carried as a private copy (and bench was about to fork as a sixth):
BuildNav over the shared config.ini with the canonical ordering and
paste/pages/hub exclusions, a per-request Page with login/logout/profile
URLs against meta's unified login, embedded srht-nav / srht-env-banner
partials (circle brand + red service label + switcher + login box), and
the generic dict/shortsha template helpers.

Policy decisions the copies had drifted on are baked in: switcher only
for authenticated viewers, hub excluded in the builder rather than the
template, profile link prefers hub's ~username page, environment name
uppercased for the banner. Service-specific needs surfaced by the cover
survey get seams instead of copies: ExtraNav for extra switcher entries,
ContainerClass for full-bleed pages, the config section as an explicit
parameter for the active check.