fix(apple-import): populate error_message on failed jobs

[shiba4life]

Summary

• Apple-import failure paths set job.status = JobStatus::Failed + job.message = ... directly, never touching job.error. The IngestionProgress::From<Job> mapping ships job.error to the API response's error_message, so every Apple-import failure surfaced error_message: null even though is_failed: true.
• Add a private mark_failed(job, msg) helper that sets all three fields atomically, then sweep the 16 failure sites in apple_import.rs (notes/reminders/photos/calendar/contacts — extraction errors, task panics, non-macOS guards, and the reminders ingestion-failure path inside build_reminders_final_job).
• Deliberately avoid Job::fail because it prepends "Failed: " to message, which would alter the user-visible status_message text (per OUT OF SCOPE: "Don't change the user-facing error text").
• Smart-folder paths already use job.fail / fail_progress and were never affected.

Before / after

// Before (contacts timeout):
{ "is_failed": true, "error_message": null,
  "status_message": "Failed to extract contacts: osascript timed out…" }

// After:
{ "is_failed": true,
  "error_message": "Failed to extract contacts: osascript timed out…",
  "status_message": "Failed to extract contacts: osascript timed out…" }

Test plan

• Strengthen reminders_final_job_tests::ingest_error_marks_failed_and_surfaces_error to assert job.error.as_deref() == Some(...). The new line fails on main and passes here — proves the regression guard.
• Add mark_failed_tests::populates_both_message_and_error to pin the helper's contract (so a future "just call Job::fail()" refactor can't silently re-introduce the "Failed: " prefix on status_message).
• cargo fmt --all -- --check clean.
• cargo clippy --workspace --all-targets clean (one pre-existing macOS-only dead_code warning unrelated to this change; CI runs on Linux where the gated function is not compiled).
• cargo nextest run --workspace --lib — 924/924 pass.
• Manual repro on the contacts/calendar timeout paths after merge — out of scope to spend bundling for this fix.

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