web: restyle dashboard and database lists after git.sr.ht

Replace the bare 'Your databases' heading and compact grid with the
git.sr.ht dashboard layout: a sidebar column with a welcome blurb plus
block buttons (create database, configure dolt credentials), and the
shared event-list cards for the database list. The repoList partial now
renders each database as an event card — name, visibility as small
muted text (non-public only, like git.sr.ht), description below — and
the profile page picks the same partial up automatically.

Adds a 'lower' template func for the visibility label and drops the now
unused .repo-list grid from main.scss (.event-list ships with the core
theme already).

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.