refactor: move KV repositories to infrastructure (Track P — points 2, 6c)

Make the domain stop depending on infrastructure ("imports point inward").

- Point 2: relocate the four KV adapters (FeedRepository, IconRepository,
  WebSubSubscriptionRepository, CountersRepository) from domain/ to
  infrastructure/, where the logger import is legitimate. The domain now keeps
  only the pure key schema (feed-keys.ts), the Feed aggregate and value objects;
  it imports nothing outward. Deliberately no hand-rolled 24-method port
  interface (YAGNI without DI) — relocation alone fixes the direction.
- Point 6c: EmailParser.extractFeedId now returns a validated FeedId value
  object instead of a raw string, so the most untrusted input (an inbound
  recipient address) is guarded at the parse boundary and no longer round-trips
  through FeedId.fromTrusted in the ingest path.

All import paths updated; CLAUDE.md source layout/KV-schema notes updated.
351 tests pass; tsc --noEmit clean.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/application/stats.ts

@@ -1,8 +1,8 @@
 import { Counters, Env, StatsResponse } from "../types";
 import { logger } from "../infrastructure/logger";
-import { FeedRepository } from "../domain/feed-repository";
-import { CountersRepository } from "../domain/counters-repository";
-import { WebSubSubscriptionRepository } from "../domain/websub-subscription-repository";
+import { FeedRepository } from "../infrastructure/feed-repository";
+import { CountersRepository } from "../infrastructure/counters-repository";
+import { WebSubSubscriptionRepository } from "../infrastructure/websub-subscription-repository";
 import { FeedId } from "../domain/value-objects/feed-id";
 import { getAttachmentBucket } from "../infrastructure/attachments";