Mobile Phase 8h: Grid detail stage/reminder cards + Open-in-Grid deep-link

Grid full-screen investor detail, conformed to the dc anatomy:
- G4: pipeline stage as a single tappable .detail-tap-card (chip + Change/Add)
- G5: dedicated Reminder card fed by the soonest active reminder; tri-state
  (loading → disabled "Checking…" so a pre-load tap can't POST a duplicate;
  none → "No reminder set"; object → edit). Edits PATCH in place, else POST.
- G6 (notes timeline) was already in place.

Open-in-Grid deep-link, now on all three mobile detail surfaces (Contacts,
Pipeline, Reminders): a shared shell openInvestorInGrid(rowId) sets a one-shot
gridUiAction object the mobile grid consumes on mount to open that investor's
detail; the desktop grid drains the unrecognized object so it can't linger.
Each surface gets its grid row id from a server-injected source_row_id:
contacts via contact_grid_signals, opportunities via the durable
fundraising_investor_id join, reminders via the investor_id join. All are
read-only/GET-only or field-allowlist writes, so none need a strip point.

Tests: source_row_id injection assertions for contacts, opportunities, and
reminders; full suite 40/40. Client surfaces jsdom-verified.

backend/test_contacts_grid_signals.py

@@ -8,7 +8,10 @@ sourced from the fundraising grid (the canonical investor model), for the mobile
   - `pipeline_stage` -> that investor's live derived stage (drives the card's stage pill),
                     or null when the investor isn't in the pipeline.
   - `priority` -> that investor's priority flag (drives the mobile Contacts Priority sort, 8d).
-A contact with no grid link (pure classic/legacy contact) gets committed 0 / stage null / priority false.
+  - `source_row_id` -> that investor's grid row id (the "Open investor in Grid" deep-link target, 8h),
+                    present for ANY grid-linked contact (even a zero-commit prospect), null otherwise.
+A contact with no grid link (pure classic/legacy contact) gets committed 0 / stage null / priority false
+/ source_row_id null.
 Signals are derived fresh on read and never stored on the contact. Synthetic data only.
 
 Run: cd backend && python3 test_contacts_grid_signals.py
@@ -148,6 +151,15 @@ def main():
         check((vince or {}).get("priority") is False,
               f"Vince.priority is False (no grid link) (got {(vince or {}).get('priority')!r})")
 
+        # ── source_row_id signal: the "Open investor in Grid" deep-link target (8h) ──
+        print("\n[source_row_id: Open-in-Grid deep-link target = the linked investor's grid row id]")
+        check((jane or {}).get("source_row_id") == "rowAcme",
+              f"Jane.source_row_id == 'rowAcme' (got {(jane or {}).get('source_row_id')!r})")
+        check((pat or {}).get("source_row_id") == "rowBeta",
+              f"Pat.source_row_id == 'rowBeta' (present for a zero-commit linked contact) (got {(pat or {}).get('source_row_id')!r})")
+        check((vince or {}).get("source_row_id") is None,
+              f"Vince.source_row_id is None (no grid link) (got {(vince or {}).get('source_row_id')!r})")
+
         # ── the get-by-id endpoint carries the same signals (mobile detail sheet, 8b) ──
         print("\n[get-by-id: /api/contacts/{id} also injects committed + pipeline_stage]")
         st, d = _req(port, "GET", f"/api/contacts/{jane['id']}", token)
@@ -193,6 +205,9 @@ def main():
         # The winning (higher-committed) link is Mega Fund LP, which is not flagged → priority follows it.
         check(jd.get("priority") is False,
               f"multi-linked contact's priority follows the higher-committed investor (Mega, unflagged) (got {jd.get('priority')!r})")
+        # The deep-link target also follows the winning link → Mega's grid row (rowMega), not rowAcme.
+        check(jd.get("source_row_id") == "rowMega",
+              f"multi-linked contact's source_row_id follows the higher-committed investor (rowMega) (got {jd.get('source_row_id')!r})")
     finally:
         httpd.shutdown()