fix: remove pre-eslint unused-variable errors across src/

Remove 21 unused imports/variables that caused eslint failures:
- actions.ts (2): Subscription type import, getCronExpression import
- alert.ts (4): CronExpressionParser, tryCatch, int, HOUR
- digest.ts (12): now, nth, nthEq, dateToSeconds, getIdFilters,
  getReplyFilters, Loader, AdapterContext, makeLoader, SocketAdapter,
  call, loadRelaySelections
- env.ts (1): netContext
- worker/email.ts (1): purgeJob variable (kept CronJob side-effect)

All unused symbols were pre-existing, not related to changed files.
tsc --noEmit passes; script/checks now returns 0 on the src check.

src/actions.ts

@@ -1,6 +1,4 @@
 import { instrument } from 'succinct-async'
-import type { Subscription } from './alert.js'
-import { getCronExpression } from './alert.js'
 import * as mailer from './mailer.js'
 import * as worker from './worker/index.js'
 import * as db from './database.js'

src/alert.ts

@@ -1,5 +1,4 @@
-import { CronExpressionParser } from 'cron-parser'
+
-import { tryCatch, int, HOUR } from '@welshman/lib'
 
 export type Subscription = {
   id: string

src/digest.ts

@@ -1,13 +1,9 @@
 import { neventEncode, decode } from 'nostr-tools/nip19'
 import {
   spec,
-  now,
   sortBy,
   groupBy,
   displayList,
-  nth,
-  nthEq,
-  dateToSeconds,
   secondsToDate,
 } from '@welshman/lib'
 import { parse, truncate, renderAsHtml } from '@welshman/content'
@@ -15,8 +11,6 @@ import {
   TrustedEvent,
   normalizeRelayUrl,
   getParentId,
-  getIdFilters,
-  getReplyFilters,
   NOTE,
   COMMENT,
   REACTION,
@@ -24,15 +18,13 @@ import {
   displayPubkey,
   getTagValue,
 } from '@welshman/util'
-import { Loader, AdapterContext, makeLoader, SocketAdapter } from '@welshman/net'
+
-import { call } from '@welshman/lib'
 import { displayDuration, createElement } from './util.js'
 import type { Subscription } from './alert.js'
 import { sendDigest } from './mailer.js'
 import { EVENT_VIEWER_URL } from './env.js'
 import {
   profilesByPubkey,
-  loadRelaySelections,
   loadProfile,
 } from './repository.js'
 

src/env.ts

@@ -1,7 +1,6 @@
 import 'dotenv/config'
 import { always } from '@welshman/lib'
 import { normalizeRelayUrl } from '@welshman/util'
-import { netContext } from '@welshman/net'
 import { Nip01Signer } from '@welshman/signer'
 import { routerContext } from '@welshman/router'
 

src/worker/email.ts

@@ -65,7 +65,7 @@ export const removeJob = (sub: Subscription) => {
 }
 
 // Daily purge of events older than 7 days
-const purgeJob = CronJob.from({
+CronJob.from({
   cronTime: '0 0 3 * * *', // 3am UTC daily
   onTick: async () => {
     const weekAgo = Math.floor(Date.now() / 1000) - 7 * 24 * 3600