feat: add stickiness round — daily Sadaqah tracker + Family Tree social loop

Two features scoped from the stickiness brainstorm, sharing one digest
notification pipeline:

Sadaqah tracker (new tab): a private daily giving journal, not a payment
processor — the app logs, it never moves money. Streak tracking follows
the proven pattern from dedicated apps (Sidq, Daily Sadaqa). Family
visibility is strictly limited to streak counts via a SECURITY DEFINER
RPC (nf_family_sadaqah_streaks) — amounts, causes, and notes never cross
the member boundary, respecting the Islamic preference for giving
privately. Entries can be dedicated 'in memory of' a deceased person from
the Family Tree, with a memorial count (nf_memorial_sadaqah_count, count
only) surfacing on that person's card.

Family Tree social loop: a 'give sadaqah in memory of' link on every
deceased person's card (cross-tab jump via a small requestedTab store in
nav.js), plus completeness hints (missing birth date, missing photo,
no relationships linked) feeding directly into the existing Coverage
Dashboard recommendations engine rather than a new UI surface.

Daily digest Edge Function + pg_cron (07:00 UTC): batches into one email
per family member per day, sent only when there's real content — tree
activity in the last 24h, a birthday/death-anniversary today, or a
weekly sadaqah recap on Sundays. An empty day sends nothing, deliberately
avoiding the notification-spam failure mode the research flagged.
Protected by a shared secret header since it's cron-invoked, not
user-triggered. Verified with a live manual invocation before relying on
the schedule.

Found and fixed two real bugs in nf_family_sadaqah_streaks during E2E
testing: an ambiguous unqualified 'member_id' column reference colliding
with the function's OUT parameter (42702), and a bigint/int type mismatch
from count(*) (42804) — both would have 400'd on every call in production.

Covered by e2e-sadaqah-tree.cjs (12/12). Full regression: 280/280 across
all suites.

src/lib/nav.js

@@ -0,0 +1,6 @@
+import { writable } from 'svelte/store';
+
+// Cross-component tab navigation — App.svelte owns the actual tab index
+// locally (not a store), so this is a one-shot request channel: set the
+// tab's display name here, App.svelte jumps to it and clears the request.
+export const requestedTab = writable(null);