Mobile Phase 8g: add-investor sheet — optional stage picker + Priority toggle + reminder

The mobile "New investor" sheet now captures three optional fields beyond name/contact/note,
matching the dc (GridApp.dc.html:737):

- Initial pipeline stage — a .stage-pick chip picker, defaulting to "Not in pipeline" so a
  plain directory add never auto-creates an opportunity row (Grant's call).
- A framed "Flag as Priority" toggle.
- An optional reminder (title + a progressive due-date field).

submitCreate orchestrates one-row calls in order: create (log-communication
create_investor_if_missing, now carrying priority) -> if a stage was picked, link to the
pipeline at that stage (reusing applyStage's idempotent link-then-PATCH) -> if a reminder
title was given, POST /api/reminders keyed on the new row's source_row_id. The link and
reminder steps are non-fatal: a failure toasts but never loses the created investor, and a
create that returns no row id warns instead of a clean success.

Backend: handle_log_fundraising_communication honors an optional priority flag only on its
create-if-missing branch (an existing-row log never touches priority).

Guarded by test_grid_add_investor.py (priority-on-create, defaults-False, the create-branch-
only invariant, and the create->link / create->reminder handshakes on a freshly-synced row).
40/40 backend green; the create sheet was interaction-verified in a throwaway jsdom harness.

backend/server.py

@@ -3341,6 +3341,9 @@ class CRMHandler(BaseHTTPRequestHandler):
         contact_in = body.get('contact')
         append_note = bool(body.get('append_note', True))
         create_investor_if_missing = bool(body.get('create_investor_if_missing', False))
+        # Optional initial Priority flag for the mobile add-investor sheet (8g). Honored ONLY on the
+        # create branch below — an existing-row log-communication never touches its priority.
+        create_priority = bool(body.get('priority', False))
         # Provenance: where this logged communication originated (grid UI vs the Matrix
         # intake bot). Default preserves prior behavior; callers may override.
         comm_source = (str(body.get('source') or 'fundraising_grid').strip() or 'fundraising_grid')[:64]
@@ -3391,7 +3394,7 @@ class CRMHandler(BaseHTTPRequestHandler):
                 "notes_last_modified": "",
                 "last_communication_date": "",
                 "lead": "",
-                "priority": False,
+                "priority": create_priority,
                 "follow_up": False,
                 "graveyard": False
             }