fix(infra): one warehouse env for every querying Worker, and small Worker fixes - #2441

🟢 Confidence 9/10 · safe to merge. The warehouse env merge only shows on a real deploy; the status cache change is pinned by three new tests.
_{no findings · tests partial −1 · risk medium}

Consolidates the five warehouse keys into clickhouseEnv bound to the API, alerting and AI Workers, caches a KV host miss in the status Worker, shares queue retry limits, and drops a dead email flag, three consumer shims and the v1 Electric shape. Safe to merge. Neither open McpQueryError nor CancellationReviewError issue is addressed by this diff.

• clickhouseEnv binds CLICKHOUSE_URL to the alerting and AI Workers
• pageIdForHost caches a KV host miss for 30 seconds
• Queue retry limits move into one queue-retry-limits module
• The v1 alert_destinations Electric shape is retired

Before merge

• Infra · Check every environment has what this config now expects · alchemy.run.ts
• Manual · Every stage that sets CLICKHOUSE_URL must let the ai and alerting Workers reach that endpoint

Production impact

_{4ed7f94 · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}