feat(speedtest): full speedtest-tracker-style automation (2.9.0)

Switch worker to the Ookla CLI (jitter, packet loss, server, ISP,
shareable result URL, bytes). Migration 028 enriches speedtest_results
+ adds a generic app_settings store. New /speedtest page: KPIs,
throughput + latency charts, window stats, configurable schedule
(reschedulable cron) & low-speed alert threshold, history table.
SV card gains ping/jitter + a link through to the page.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/db/migrations/028_speedtest_metrics.sql

@@ -0,0 +1,22 @@
+-- 028_speedtest_metrics.sql
+-- Enrich speedtest results with the full Ookla metric set + a generic settings
+-- store (reused by the speedtest schedule and, later, theming).
+ALTER TABLE speedtest_results ALTER COLUMN down_mbps DROP NOT NULL;
+ALTER TABLE speedtest_results ALTER COLUMN up_mbps   DROP NOT NULL;
+ALTER TABLE speedtest_results
+  ADD COLUMN IF NOT EXISTS jitter_ms   numeric,
+  ADD COLUMN IF NOT EXISTS packet_loss numeric,
+  ADD COLUMN IF NOT EXISTS server_name text,
+  ADD COLUMN IF NOT EXISTS server_id   text,
+  ADD COLUMN IF NOT EXISTS isp         text,
+  ADD COLUMN IF NOT EXISTS result_url  text,
+  ADD COLUMN IF NOT EXISTS down_bytes  bigint,
+  ADD COLUMN IF NOT EXISTS up_bytes    bigint,
+  ADD COLUMN IF NOT EXISTS ok          boolean NOT NULL DEFAULT true,
+  ADD COLUMN IF NOT EXISTS error       text;
+
+CREATE TABLE IF NOT EXISTS app_settings (
+  key        text PRIMARY KEY,
+  value      jsonb NOT NULL DEFAULT '{}'::jsonb,
+  updated_at timestamptz NOT NULL DEFAULT now()
+);