Alloy V1.16.0 (#345)

Bump Grafana Alloy v1.14.0 → v1.16.0 across all four services (alloy-k8s, alloy-ringtail, alloy-tracing-ringtail; alloy native ansible). Also migrate the indri build path from `Dockerfile` to a native Dagger `container.py` per the build-container-image migration playbook.

## Highlights from upstream
- v1.15: database observability promoted to stable, OTel Collector → v0.147.0
- v1.16: clustering for `loki.source.kubernetes_events`, MySQL exporter 0.19.0
- One pre-existing breaking change in v1.15 (`loki.source.awsfirehose` undocumented metric prefix rename) — not used here.

## Build infra
Alloy v1.16.0's go.mod requires Go 1.26.2. The nix derivation now uses `pkgs.go_1_26` with `GOTOOLCHAIN=local` to avoid auto-downloading a toolchain blob that violated the fixed-output rule.

## Test plan
- [ ] CI: `mise run container-build-and-release alloy --ref alloy-v1.16.0` (dispatched as run 522; nix job to be re-triggered with the v1.16.0 goModules outputHash once the local ringtail build surfaces it)
- [ ] After CI green, bump `images[].newTag` in three kustomizations to the new `-<sha>` and `-<sha>-nix` tags, deploy from this branch via `argocd app set <app> --revision alloy-v1.16.0 && argocd app sync <app>`
- [ ] Manual rebuild of macOS native binary on gilbert (per ansible/roles/alloy README) and `mise run provision-indri -- --tags alloy --check --diff`
- [ ] `mise run services-check` after merge & redeploy

Reviewed-on: #345

service-versions.yaml

@@ -72,22 +72,22 @@ services:
 
   - name: alloy-tracing-ringtail
     type: argocd
-    last-reviewed: 2026-03-13
-    current-version: "v1.14.0"
+    last-reviewed: 2026-04-30
+    current-version: "v1.16.0"
     upstream-source: https://github.com/grafana/alloy/releases
     notes: Privileged DaemonSet with Beyla eBPF for HTTP tracing on ringtail
 
   - name: alloy-ringtail
     type: argocd
-    last-reviewed: 2026-03-13
-    current-version: "v1.14.0"
+    last-reviewed: 2026-04-30
+    current-version: "v1.16.0"
     upstream-source: https://github.com/grafana/alloy/releases
     notes: DaemonSet on ringtail for host metrics and pod logs
 
   - name: alloy-k8s
     type: argocd
-    last-reviewed: 2026-03-13
-    current-version: "v1.14.0"
+    last-reviewed: 2026-04-30
+    current-version: "v1.16.0"
     upstream-source: https://github.com/grafana/alloy/releases
 
   - name: tailscale-operator
@@ -338,8 +338,8 @@ services:
 
   - name: alloy
     type: ansible
-    last-reviewed: 2026-03-13
-    current-version: "v1.14.0"
+    last-reviewed: 2026-04-30
+    current-version: "v1.16.0"
     upstream-source: https://github.com/grafana/alloy/releases
     notes: Built from source on indri