web: mirror the git twin's description onto companion databases

The internal create endpoint accepts a description, but its only caller
— dolt-git-hook — never sends one: git.sr.ht's push context does not
carry it. Companion databases therefore all sat descriptionless on the
dashboard while their git twins had perfectly good descriptions.

Resolve the description server-side instead: a GitDescriber dependency
(internal GraphQL query to git.sr.ht in the owner's name, the same
network-key trust the hook uses to reach us, pointed the other way) is
consulted on every /internal/repos call. A fresh companion is created
with the twin's description; for an existing one the push doubles as the
sync point — a changed, non-empty git description overwrites the stored
one. An empty git description never clobbers one set in dolt's own
settings, and every failure mode (no twin, git.sr.ht down, no resolver
wired) degrades to no mirroring. The lookup is capped at 3s so the
hook's own 5s POST timeout is never exceeded.

Adds testify as a direct dependency for the new tests.

doltsrht: pass full os.Args to server.New so -b binds the web listener

getopt skips argv[0] as the program name, so os.Args[1:] made it swallow the
first real flag (-b) and silently fall back to defaultWebAddr (localhost),
leaving the web UI unreachable from Traefik. Match compare/upstream: pass os.Args.

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

cmd: doltsrht and doltsrht-migrate binaries, module tidy