Remove Instructions/Feedback + lp_profiles; sync retry, purge, mobile fixes (v0.1.0:104)

Removals (net -570 lines):
- Delete the Instructions and Feedback (feature_requests) pages + backend.
- Retire lp_profiles + investor_type across server, ingest, and seeds; migration
  0008 drops both empty tables (a sanctioned one-off exception to
  never-hard-delete). 0001's lp_profiles ALTER is removed so a fresh DB doesn't
  break the migration chain (live DBs already applied it).

Fixes:
- Email sync: a transient timeout no longer terminally parks a mailbox; the
  scheduler retries 'retrying' each cycle and re-includes errored accounts on an
  hourly backoff, so stuck mailboxes self-heal.
- Mobile Contacts: page through the full directory (server caps 500/page) -- one
  fetch silently truncated at 720, hiding people from the list and from search.
- Mobile email review: clock icon to set a reminder inline; approval cards show
  date/time.

New:
- Admin-only purge of soft-deleted rows (Settings -> Admin; type-to-confirm,
  refuses any row still linked to live data).

Tests: 45/45 (adds test_sync_ready + test_purge_soft_deleted). Reviewer pass
applied (NULL reminders.contact_id on contact purge). Bumped to v0.1.0:104.

backend/migrations/0001_phase0_foundation.sql

@@ -113,4 +113,8 @@ ALTER TABLE contacts       ADD COLUMN deleted_at TEXT;
 ALTER TABLE organizations  ADD COLUMN deleted_at TEXT;
 ALTER TABLE opportunities  ADD COLUMN deleted_at TEXT;
 ALTER TABLE communications ADD COLUMN deleted_at TEXT;
-ALTER TABLE lp_profiles    ADD COLUMN deleted_at TEXT;
+-- lp_profiles ALTER removed (v0.1.0:104): the lp_profiles table is dropped in
+-- 0008_drop_retired_tables.sql and is no longer created by init_db(), so this
+-- ALTER would fail "no such table" on a fresh install. Live DBs already applied
+-- this migration (with the original ALTER) before lp_profiles was dropped, so
+-- removing the line here only affects fresh DBs — same end state either way.