refactor: separate Feed domain state from persistence DTO

Move four DDD tensions on the Feed aggregate to ground:

- #1 The aggregate now holds a domain FeedState (camelCase) instead of the
  snake_case FeedConfig DTO; infrastructure/feed-mapper.ts owns the
  FeedState<->FeedConfig/FeedListItem translation as the sole snake_case site
  outside the HTTP edge.
- #3 Replace the edit() recomputeExpiry control flag with a Lifetime VO:
  passing a lifetime recomputes expiry, omitting it preserves the current one
  (the dashboard quick-edit path).
- #4 Domain events carry their own feedId; dispatchFeedEvents centralizes the
  drain+dispatch in the application layer (no more manual pullEvents at call
  sites), keeping infra->application dependency direction intact.
- #6 Rename FeedId.fromTrusted to FeedId.unchecked to make the absence of
  revalidation explicit.

Adds Lifetime + feed-mapper round-trip tests. 353 tests green, tsc clean,
wrangler dry-run OK. Docs (CLAUDE.md) synced.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/domain/value-objects/lifetime.ts

@@ -0,0 +1,32 @@
+const HOUR_MS = 3_600_000;
+
+/**
+ * A feed's lifetime as a value object: either a positive number of hours or
+ * "never". `resolveExpiry(now)` turns it into an absolute `expires_at` instant
+ * (or undefined for a feed that never expires).
+ *
+ * Which lifetime applies — client request vs. server-side `FEED_TTL_HOURS`
+ * override — is the application layer's policy; it builds the VO and hands it to
+ * the aggregate. The aggregate never parses env config or reaches for a clock to
+ * compute expiry itself.
+ */
+export class Lifetime {
+  private constructor(private readonly hours: number | undefined) {}
+
+  /** A finite, positive lifetime. Non-positive/non-finite inputs collapse to never. */
+  static ofHours(hours: number): Lifetime {
+    return new Lifetime(hours);
+  }
+
+  /** A feed that never expires. */
+  static readonly never = new Lifetime(undefined);
+
+  /** The absolute expiry instant for this lifetime, or undefined if it never expires. */
+  resolveExpiry(now: number): number | undefined {
+    return this.hours !== undefined &&
+      Number.isFinite(this.hours) &&
+      this.hours > 0
+      ? now + this.hours * HOUR_MS
+      : undefined;
+  }
+}