chrome: link the favicon through the shared head partial

The icon href was a literal in the layout, so a build with no static tree — a
test, a binary run out of a working copy — asked for /static/logo.svg once per
page and got a 404 each time. It is the chrome's FaviconHref now: our own logo
when this build ships one, checked the way the stylesheet already was, and
NewService's built-in data: URI when it does not. Both <link>s come from
srht-head-links, so the guard against <link href=""> is written once.

Also pins what the repo-list partial's optional fields do for a service that has
no timestamp in its schema: a card with no muted footer, not "0001-01-01".

web: render through ecore's pages and its error page

The page list, the per-page parse loop and the view-template loop are
gone: pages discovers every file in templates/, so a page is registered
by existing, and one that defines no content block is refused at startup
rather than served as chrome around a hole. 404.html and 403.html are
gone with them — the shared error page carries the same body, and its
prose is deliberately the same for a database that is not there and one
the viewer may not see.

The renderer that replaced them closes a leak: the old one wrote
"template render error: "+err.Error() into the response body, handing
the viewer template names and field paths. pages answers a fixed
sentence and returns the error for the log.

reltime and abstime come from chrome.Funcs now; ours called every future
instant "just now", where the shared one says "in 3 weeks".

web: draw the chrome from sr-ht-ecore

The brand, the service switcher, the login block, the environment banner
and the database listing were a local port of core.sr.ht's nav — one of
five such ports on this instance, and they had already drifted. They are
now sourcecraft.dev/bigbes/sr-ht-ecore/chrome, the one copy every custom
service draws from.

Deleted: web/chrome.go entire (navEntry, networkOrder, networkExcluded,
buildNetwork, basePage, loginURL, logoutURL), templates/nav.html,
templates/icons/circle.svg (ecore inlines the identical SVG), the
repoList partial, and the local dict/shortHash duplicates.

Added: one chrome.Service built in newApp from our config section with
the hashed stylesheet href set on it, a chrome.Page per request through
app.page, chrome.Attach on every template set, and chrome.Funcs as the
base of the funcmap. Handlers embed chrome.Page in their view structs
instead of copying its fields; the row browser sets ContainerClass to
container-fluid, since its column count is the table's and not ours.

Three behaviour changes come with ecore's policy, all deliberate: the
profile link now prefers hub's ~username page when hub.sr.ht is
configured (it was always meta's /profile), the brand carries a fixed
15rem min-width so the switcher starts at the same x on every service,
and a binary built without a stylesheet renders bare rather than linking
an empty href. The nav test went with the code it tested — ordering,
exclusions and login URLs are ecore's to cover — and what replaced it
asserts only what is ours: that pages are drawn through the chrome at
all, and that the row browser is full-bleed.

The auth path is untouched: a foreign bearer token is still accepted as
a meta.sr.ht PAT.

web: router, handlers, and sourcehut chrome

Chi route table per plan, SourceHut chrome port (nav/layout from
core.sr.ht Bootstrap structure), dual-flow clone box, dolt-key
association page with hash-fragment prefill, same-origin CSRF checks.
Handlers depend on small injected interfaces (StoreManager, RepoStore,
BrowseOpener, UserResolver) with production adapters included.