fix(activity-feed): hide pipeline-attributed events from public timeline

After canonicalizing submitted_by (PRs #9, #10, #11), reweave/* and
ingestion/* PRs now correctly carry submitted_by=pipeline. They show up
in the activity feed as a contributor row that has no /contributors/
profile page (pipeline does not meet the min_claims floor), so clicks
404.

Reweave/ingestion are pipeline housekeeping — graph re-knitting and
external source ingestion run by the daemon, not contributions. The
feed already filters commit_type=pipeline via _FEED_COMMIT_TYPES; this
extends the same intent along the contributor axis.

Internal diagnostics, CI math, and contribution_events are unaffected
— only the public timeline drops these rows.

Verified locally against 1972 events: 0 pipeline rows remain in
output, contributors are leo/vida/clay/rio/theseus/astra/m3taversal.

diagnostics/activity_feed_api.py

@@ -225,6 +225,15 @@ def _build_events():
                 continue
 
             contributor = _normalize_contributor(row["submitted_by"], row["agent"])
+            # Hide pipeline-attributed events (reweave/*, ingestion/*) from the
+            # public activity feed. They're automation maintenance, not
+            # contributions — the daemon re-knits the graph nightly and ingests
+            # external sources. Internal diagnostics + CI math still see these
+            # rows in prs / contribution_events; only the public timeline drops
+            # them. Mirrors the existing _FEED_COMMIT_TYPES filter (which hides
+            # commit_type='pipeline') along the contributor axis.
+            if contributor == "pipeline":
+                continue
             merged_at = row["merged_at"] or ""
             domain = row["domain"] or "unknown"
             kind = _KIND_MAP.get(event_type, event_type)