Add frigate-notify nix container build (#339)

## Summary
- Mirrors `github.com/0x2142/frigate-notify` at `v0.5.4` to `forge.ops.eblu.me/mirrors/frigate-notify`.
- Adds `containers/frigate-notify/default.nix` — `buildGoModule` + `dockerTools.buildLayeredImage`, following the `ntfy` pattern.
- Uses `-tags goolm` to avoid the libolm CGO dependency (matrix notifier is imported unconditionally in the upstream but we only use ntfy alerts).
- Runs as nonroot (UID 65534), exposes port 8000, bundles `cacert`/`tzdata`.

## Why
Move `ghcr.io/0x2142/frigate-notify:v0.5.4` (ringtail-deployed) under local control. Aligns with the [[indri → ringtail migration plan]] and the `default.nix` convention for ringtail-targeted containers documented in [[build-container-image]].

## Verification
- `dagger call build-nix --src=. --container-name=frigate-notify export --path=./out.tar.gz` produces a valid 20MB docker archive (10 layers) with `blumeops/frigate-notify` tag locally.
- Hashes pinned for `fetchgit` (src) and `vendorHash` (go modules).

## Follow-up (post-merge)
1. `mise run container-build-and-release frigate-notify` — release from main SHA.
2. C0 follow-up: update `argocd/manifests/frigate/kustomization.yaml` image ref to `registry.ops.eblu.me/blumeops/frigate-notify:v0.5.4-<sha>-nix`.
3. ArgoCD auto-syncs the deployment.

## Test plan
- [ ] `dagger call build-nix` succeeds from a clean checkout.
- [ ] `mise run container-build-and-release frigate-notify --dry-run` looks correct.
- [ ] After release + kustomization swap: frigate-notify pod comes up healthy on ringtail; ntfy alerts still fire on Frigate events.

Reviewed-on: #339

containers/frigate-notify/default.nix

@@ -0,0 +1,57 @@
+# Nix-built frigate-notify — polls Frigate webapi and pushes alerts to ntfy.
+{ pkgs ? import <nixpkgs> { } }:
+
+let
+  version = "0.5.4";
+
+  src = pkgs.fetchgit {
+    url = "https://forge.ops.eblu.me/mirrors/frigate-notify.git";
+    rev = "v${version}";
+    hash = "sha256-c/QOSQNNJ+ElMDm45lBOsru/ujBhCWethiRefj3hBOk=";
+  };
+
+  frigate-notify = pkgs.buildGoModule {
+    inherit src version;
+    pname = "frigate-notify";
+
+    vendorHash = "sha256-Ho9oaK01wJDPf3ufV2klV1dG4qFNVNJkWmWvEgAy10s=";
+
+    doCheck = false;
+    subPackages = [ "." ];
+
+    # `goolm` swaps the matrix crypto backend from libolm (CGO) to pure-Go olm,
+    # avoiding the libolm.h dependency. Our deployment doesn't use matrix, but
+    # the package is imported unconditionally.
+    tags = [ "goolm" ];
+
+    ldflags = [ "-s" "-w" ];
+
+    meta = with pkgs.lib; {
+      description = "Bridge between Frigate NVR events and notification services";
+      homepage = "https://github.com/0x2142/frigate-notify";
+      license = licenses.mit;
+      mainProgram = "frigate-notify";
+    };
+  };
+in
+
+pkgs.dockerTools.buildLayeredImage {
+  name = "blumeops/frigate-notify";
+  contents = [
+    frigate-notify
+    pkgs.cacert
+    pkgs.tzdata
+  ];
+
+  config = {
+    Entrypoint = [ "${frigate-notify}/bin/frigate-notify" ];
+    Env = [
+      "SSL_CERT_FILE=${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt"
+      "TZDIR=${pkgs.tzdata}/share/zoneinfo"
+    ];
+    ExposedPorts = {
+      "8000/tcp" = { };
+    };
+    User = "65534";
+  };
+}