login: ecore's cookie decoder, which validates the name ours did not

authz/identity.go was the fifth copy of a decode the instance has one of,
and it was one of the two that validated nothing: whatever name a sealed
payload carried went on to the GraphQL viewer field, the chrome's nav and
every log line the request produced. login.ValidName refuses it, and
there is no spelling of the API that turns the check off.

Gone with it: CookieName, UsernameFromRequest, Middleware, ForContext and
the ctxKey, plus identity_test.go, whose round-trip, tilde-stripping and
garbage-cookie cases are ecore's tests now. The Middleware becomes
login.Optional() — this service refuses nobody, git.sr.ht decides what an
anonymous viewer may see — and the default validator is kept rather than
core.ValidOwner, which is lowercase-only and would log a real account out
of compare alone.

The one behaviour change a viewer could notice: a cookie whose name
carries a '/', a control byte or a non-ASCII letter now reads as
anonymous instead of as that name.

readme: name the ecore packages the web tier draws from

web: draw the chrome from sr-ht-ecore

The nav/service-switcher, the brand, the login block and the environment
banner were a copy of code every custom service on this instance carries.
The copies drifted, so they now come from one place:
sourcecraft.dev/bigbes/sr-ht-ecore/chrome.

web/chrome.go is gone. New builds one chrome.Service from the shared
config.ini and hands it the discovered stylesheet; view() asks it for a
chrome.Page per request, which viewData embeds rather than copies, so a
field ecore adds later arrives here without an edit. The layout invokes
"srht-env-banner" and "srht-nav" instead of the markup it used to spell
out, the landing's repository listing goes through "srht-repo-list", and
the FuncMap starts from chrome.Funcs() with the local shortsha deleted.

Two ecore policies differ from what this service did and are adopted as
the instance's: the brand label is the config section's short name rather
than a literal "compare", and the origins are trimmed of a trailing
slash. What stays local is what is compare's alone: the bundle href, the
diff-status colours, and the container-fluid the two diff views ask for.

Tests move to testify; the nav ordering/exclusion test goes with the code
it tested, and a test that the layout invokes the chrome at all replaces
it.

web: content-hash the bundle and colour the status column

Two diff-view fixes reported against the deployed instance.

Empty file tree after an upgrade: bundle.js had a stable filename served with a
1-hour cache, so browsers kept a pre-fix bundle and the @pierre/trees sidebar
rendered blank. Content-hash the bundle like the stylesheet — Makefile emits
bundle.<sha256[:8]>.js, server.go globs it into a BundleHref, the templates
reference {{.BundleHref}}, and the hashed name is served immutable. A deploy now
always busts the cache.

Unreadable status column: the changed-files table rendered A/M/D in the dim
default cell colour, near-invisible on the dark chrome. Render each status as a
semantic .diff-status badge (added=green, modified=amber, deleted=red,
renamed=blue) with light/dark variants, via statusClass/statusLabel helpers and
a small self-contained style block (the sourcehut-derived main.min.css can't be
rebuilt locally).

Tests resolve the hashed bundle via a bundleName helper and assert its immutable
cache header; docs updated for the hashed filename.

docs: note that static assets are embedded and need a rebuild

web/static is //go:embed-ed into the binary, so `make css`/`make bundle` alone
don't reach the running daemon — re-run `make build` after either. Documents the
stale-asset gotcha in the build section.

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

go.mod: tidy and complete the README

go mod tidy promotes fernet-go and vaughan0/go-ini from indirect to
direct (the cmd entry point imports go-ini and the smoke test imports
fernet) and drops stale transitive checksums for AWS S3/CLI packages that
core-go pulls but compare.sr.ht never imports. The require block is
otherwise unchanged; build and tests stay green.

README: correct the architecture to reflect the go-git in-process backend
(no runtime git shell-out), document the full local development recipe
(config.ini template, key generation, dev-stub, forging a login cookie),
the deployment steps (install, config propagation for nav, DNS,
internal-ipnet, nginx, User=git systemd), and design notes recording the
go-git decision, the 10 MB bundle rationale, and the pending LICENSE.

compare.sr.ht: project foundation — core package, build scaffolding, core-go fork pin

Bootstrap the go.bigb.es/sourcehut-compare service:

- go.mod (go 1.26.4) pinning core-go to the private fork
  git.srht.bigb.es/~bigbes/core-go @ c2c2f3848fa9 via a replace directive;
  go.sum populated by a throwaway smoke build importing core-go
  config/crypto/client/server + chi + logrus (gates API drift from the
  verification baseline fdb3662 to upstream 71b2787).
- core/: pure domain package — sentinel errors, owner/repo/ref validation
  (check-ref-format-style, hostile-input hardened), and the compare-spec
  grammar (ParseCompareSpec, three-dot/two-dot, percent-unescape). Table
  tests at 97% coverage.
- Makefile (all/build/test/css/bundle/run-dev/install), config.example.ini
  documenting the shared keys read in place, contrib/ nginx block and
  systemd unit, README skeleton, .gitignore.

core-go dep deps and go mod tidy are deferred to later phases per plan.