next -> main (1.0.0 milestone) (#105)

Accumulating milestone branch. One squashed commit per closed issue; `next` is kept green and mergeable to `main` at any time without notice.

Landed so far:

- `chore: update golangci-lint to v2.12.2 with canonical config` (#54) — canonical v2-schema `.golangci.yml`, pins bumped in `Dockerfile` and `script/bootstrap`, tree at `0 issues.`. Three behaviour deltas are recorded in that PR's body: `Cache.StoreVariant` takes a context, `MetadataStorage.Store` no longer leaks temp files on failure, and the `signing_key` too-short error text gained a `value too short:` prefix.

Sequencing for the milestone is tracked in #103.

Reviewed-on: #105
Co-authored-by: clawbot <clawbot@noreply.example.org>

internal/server/routes.go

@@ -56,7 +56,8 @@ func (s *Server) SetupRoutes() {
 	s.router.Head("/v1/image/*", s.h.HandleImage())
 
 	// Encrypted image URL route
-	// The trailing filename (e.g., /img.jpg) is ignored but helps browsers with content type
+	// The trailing filename (e.g., /img.jpg) is ignored but helps
+	// browsers with content type
 	s.router.Get("/v1/e/{token}/*", s.h.HandleImageEnc())
 
 	// Metrics endpoint with auth