fix(activity-feed): canonicalize contributor handle so profile links resolve

The activity feed was returning decorated strings like "Vida (self-directed)"
and "@m3taversal" in the contributor field. The frontend uses that field as
both display label and routing handle, so /contributors/Vida%20(self-directed)
404s — Next fires notFound() in [handle]/page.tsx.

Root cause: _normalize_contributor only stripped @ and whitespace; it did not
lowercase or strip the " (self-directed)" suffix that extract.py and the
older backfill_submitted_by.py wrote into prs.submitted_by. Mixed-case
agent names (Vida vs vida) and pipeline decorators ("pipeline (reweave)")
both fell through.

Fix: lowercase + strip any trailing parenthetical decorator. Valid handles
match ^[a-z0-9][a-z0-9_-]{0,38}$ per attribution._HANDLE_RE and cannot
contain parens, so the strip is lossless.

DB simulation against 3612 merged-PR events: 0 orphan handles after
normalization (was 12 orphan label-variants before).

No KB writes — pure read-side normalization in the API layer.

diagnostics/activity_feed_api.py

@@ -129,12 +129,33 @@ def _github_pr_url(github_pr):
     return f"https://github.com/living-ip/teleo-codex/pull/{github_pr}"
 
 
+# Canonicalize contributor labels so frontend links resolve to real
+# /contributors/{handle} pages. Pipeline writers (extract.py, manual edits,
+# the old backfill_submitted_by.py) historically wrote mixed-case agent
+# names with a trailing decorator into prs.submitted_by — e.g.
+# "Vida (self-directed)", "pipeline (reweave)", or "@m3taversal".
+# These decorated strings do not exist as contributors and 404 the profile
+# page. Strip the trailing parenthetical wholesale: valid handles match
+# ^[a-z0-9][a-z0-9_-]{0,38}$ (see pipeline/lib/attribution._HANDLE_RE) and
+# cannot contain parens, so this is lossless.
+_TRAILING_PAREN_RE = re.compile(r"\s*\([^)]*\)\s*$")
+
+
+def _canonicalize(raw):
+    if not raw:
+        return ""
+    h = raw.strip().lower().lstrip("@")
+    h = _TRAILING_PAREN_RE.sub("", h).strip()
+    return h
+
+
 def _normalize_contributor(submitted_by, agent):
-    if submitted_by and submitted_by.strip():
-        name = submitted_by.strip().lstrip("@")
+    name = _canonicalize(submitted_by)
+    if name:
+        return name
+    name = _canonicalize(agent)
+    if name and name != "pipeline":
         return name
-    if agent and agent.strip() and agent != "pipeline":
-        return agent.strip()
     return "pipeline"