Add Convex backend tests for listLinkedSignalsForProject covering:
- Per-issue grouping with correct source counts
- Project membership/authz (denies non-member access)
- Cross-project signal suppression (project1 cannot see project2 signals)
- Multi-source signal source-count accuracy
- Empty project returns empty record
- Issues without linked signals are omitted from result
Make linked signals deterministically ordered newest-first within
each issue group via toSorted(createdAt descending).
Replace the deliberate signalCount of 0 with authenticated linked-Signal
data from the Lane A signalIssueAttachments relation.
- Add listLinkedSignalsForProject query (user-authenticated via
requireProjectMember) returning issue-grouped LinkedSignalView data
using the existing by_issue index. One query serves both card counts
and expanded detail.
- Update work-unit-projection builders to accept linkedSignals param;
LinkedSignal type with signalId, title, summary, sourceCount, createdAt.
- Feed real attachment data into collapsed card signalCount and expanded
detail linked-signal list with provenance (source count, relative time).
- Add signal.attached event handler to activity timeline projection.
- 32 tests including 4 linked-signal projection tests, 1 signal.attached
activity mapping test, and cross-issue signal isolation test proving
issue A cannot inherit issue B's linked signals.
