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 <noreply@anthropic.com>

src/infrastructure/favicon-fetcher.ts

@@ -4,9 +4,9 @@ import {
   ICON_TTL_SECONDS,
   MAX_ICON_BYTES,
 } from "../config/constants";
-import { IconRepository } from "../domain/icon-repository";
+import { IconRepository } from "./icon-repository";
 import { EmailAddress } from "../domain/value-objects/email-address";
-import { logger } from "../infrastructure/logger";
+import { logger } from "./logger";
 
 interface IconRecord {
   data: string | null; // base64 icon bytes, or null for a negative cache entry