Isolate per-source failures during sync

[ctrlaltdylan]

Problem

Running mrrmaid sync when one source has invalid credentials crashed the whole command with a raw traceback — even if another source was configured correctly. In practice this showed up as a Shopify 404 Client Error (from leftover placeholder creds like SHOPIFY_ORGANIZATION_ID=a) aborting a sync that only needed Stripe.

Root cause: sync_all called each source's sync unguarded, so the first exception propagated all the way up.

Change

• DataSyncService.sync_all now syncs each source independently and returns (results, errors) — successes keep their record counts, failures are captured per source ("shopify" / "stripe") with their message.
• The sync CLI prints a clean per-source warning, still renders the results table for sources that succeeded, and exits non-zero only when every configured source failed.

Before → after (bad Shopify creds + valid Stripe):

# before: full Rich traceback, Stripe never syncs, exit code from crash
# after:
⚠ Shopify sync failed: 404 Client Error: Not Found for url: https://partners.shopify.com/a/api/2026-01/graphql.json
        Sync Results
┏━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━┓
┃ Source                ┃ Records ┃
┡━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━┩
│ Stripe Subscriptions  │ …       │
└───────────────────────┴─────────┘

Tests

tests/test_sync_error_isolation.py:

• Shopify failure doesn't block Stripe (and is reported as an error).
• Stripe failure doesn't block Shopify.
• An unconfigured (None) source is skipped — neither a result nor an error.

$ python -m pytest tests/ -q
5 passed

Also manually verified end-to-end: a bad Shopify + bad Stripe config now prints two warnings + All configured sources failed to sync. and exits 1, with no traceback.

🤖 Generated with Claude Code