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).

foundation: module, core domain, schema, spike-verified dolt interop

Phase 0 foundation for dolt.sr.ht (pure-Go Dolt hosting for SourceHut).

Dependency pins:
- core-go v0.0.0-20260520082310-fdb3662452dc: the production instance's
  submodule commit (fdb3662); must never be upgraded so token/config/crypto
  behavior matches the rest of the instance.
- dolthub/dolt/go v0.40.5-0.20260626152440-45335d44ad79: pseudo-version at the
  commit tagged v2.1.10 (45335d44), matching the installed dolt CLI. The /go
  submodule's latest tag (v0.40.4, 2021) does not interop with a modern CLI;
  matching the CLI commit guarantees a common NBS format (Format_DOLT) and
  remotesapi proto.
- gopkg.in/go-jose/go-jose.v2 v2.6.3: same JOSE version dolt's creds package
  signs EdDSA keypair JWTs with, avoiding a duplicate JOSE lib.
- grpc v1.79.3, logrus v1.8.3, lib/pq v1.10.9, chi/v5 v5.3.1, brant v0.5.1.

Contents:
- core/ pure domain: models, ValidateName/ParseRepoPath, the access matrix
  (Allowed + NotFoundForPrivate), full table-driven tests.
- schema.sql + migrations/0001_initial.sql (brant format).
- config.example.ini, contrib/dolt.sr.ht.conf (nginx), Makefile, scss/main.scss,
  static/logo.svg, README, .gitignore.
- internal/smoke: throwaway import-and-build check (deleted in Phase 3).

Spike (storage/spike_test.go, tag `spike`): bare NBS store via WriteEmptyRepo,
served by remotesrv on an ephemeral single port, round-tripped through the real
dolt CLI v2.1.10 (clone -> insert -> commit -> push -> re-clone -> verify rows).
Green, no version juggling needed beyond selecting the v2.1.10 commit. FS must
be rooted at the repos dir (LocalFilesysWithWorkingDir) so sealed chunk-URL
prefixes are clean relatives.

Build note: dolt pulls go-icu-regex (CGO), which needs ICU4C headers; on this
Mac set CGO_CPPFLAGS/CGO_LDFLAGS to icu4c@78 (documented in README).