fix(metadata): stop hardcover sync colliding on reading attempt read ids

Read selection was positional: prefer any open remote read, else a cached book-level id, else the
first read returned, while the primary attempt was re-derived each sync from book dates. The two
could disagree, assigning one Hardcover read to two attempts and violating
reading_attempts_external_uidx, which aborted the sync and persisted the failure.

Treat reading_attempts.external_id as the mapping of record: an attempt keeps the read it owns, an
unlinked attempt adopts only an unclaimed read and claims it locally before the remote write, and a
fresh read is minted when nothing is adoptable. Never merge or delete attempts to resolve a
conflict, and keep soft-deleted ids reserved so importExternalRead tombstones still hold.

Also skip the link write when an attempt already owns its read, and map the aggregated attempt
timestamp to a Date so change detection stops comparing a driver string against lastSyncedAt.

Closes #907

scripts/e2e/suite-registry.mjs

@@ -285,6 +285,27 @@ export const E2E_SUITES = Object.freeze({
       ...SHARED_DB_AND_HELPER_PATHS,
     ],
   },
+  "reading-attempts": {
+    id: "reading-attempts",
+    name: "Reading Attempts",
+    timeout: 120,
+    lane: "full",
+    description: "Reading attempt lifecycle, external read identity, and Hardcover read ownership suite",
+    vitestTarget: "test/reading-attempts.e2e-spec.ts",
+    junitOutput: `${TEST_RESULTS_DIR}/reading-attempts-e2e-junit.xml`,
+    prepareDedicatedDatabase: true,
+    useDedicatedDatabase: true,
+    changedPaths: [
+      "server/src/modules/user-book-status/**",
+      "server/src/modules/hardcover/**",
+      "server/src/modules/dashboard/**",
+      "server/test/reading-attempts.e2e-spec.ts",
+      "server/test/e2e/**",
+      ".github/workflows/e2e-runner.yml",
+      "packages/types/src/book.ts",
+      ...SHARED_DB_AND_HELPER_PATHS,
+    ],
+  },
   "book-api-contract": {
     id: "book-api-contract",
     name: "Book API Contract",