pages: read forms through FormValues

Every mutation on this surface read its fields with r.PostFormValue after a bare
r.ParseForm. PostFormValue was already the right half — r.Form would merge the
query string into the body, which would let a mutation be driven from a URL
somebody was linked to, and that request is exactly the one the same-origin
guard sees nothing wrong with — but the body was bounded only by net/http's
10 MiB default, on pages anyone can reach. FormValues is both properties in one
call, and the values are passed down explicitly instead of each sub-handler
reaching back into the request.

web: guard mutations with ecore's csrf, cache and panic middleware

checkSameOrigin and originMatches are gone, and with them the three
per-handler calls that had to be remembered: csrf.Require sits over the
whole browser group, so the mutating route added next year is guarded by
being routed. The internal provisioning endpoint stays outside that
group deliberately — it is a service-to-service POST with no Origin and
its own network-key guard.

middleware.PrivateCache marks every page as one no cache may reuse for
the next viewer, which is only correct because the static handler opts
out per asset once it has found the file. RecoverPanics answers a panic
with the error page, and one that arrives after the response has started
by dropping the connection rather than appending an error to half a
document.

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.

rename module to sourcecraft.dev/bigbes/sr-ht-dolt; depend on sourcecraft sr-ht-core

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.