Bump phoenix_live_view to 1.2.12, closing last security advisory

The microprints git dep now allows phoenix_live_view ~> 1.2, so the
app can take the CVE-2026-64941 fix (open redirect in
validate_local_url!/2, fixed in 1.2.9). No 1.1.x backport existed.

blogex test lock follows to 1.2.12 so the library is tested against
the version the app ships with. mix deps.get now reports zero
security advisories.

app/mix.exs

@@ -48,7 +48,7 @@ defmodule Firehose.MixProject do
       {:postgrex, ">= 0.0.0"},
       {:phoenix_html, "~> 4.1"},
       {:phoenix_live_reload, "~> 1.2", only: :dev},
-      {:phoenix_live_view, "~> 1.1.0"},
+      {:phoenix_live_view, "~> 1.2"},
       {:lazy_html, ">= 0.1.0", only: :test},
       {:phoenix_live_dashboard, "~> 0.8.3"},
       {:esbuild, "~> 0.10", runtime: Mix.env() == :dev},