v10.24.0 archive-side embedding lifecycle: no more tier-2 leaks

Driven by a forensic audit of the prod embedding-row lifecycle (the open item
from the 10.19.0 coherence check's first prod run): 51 archived memories had
no tier-2 vector, clustered exactly on consolidation days; 3 orphan arch rows
survived hard-deleted memories; embed_meta tables created before the
localtime DDL still carried a UTC embedded_at default, making synchronous
embeds look hours older than their memory's creation.

Fixed

• Consolidation archived memories without moving their vectors. Both raw
  status-UPDATE sites in phases (merge, supersede) now go through a new
  archive_memory(conn, mid, tag_suffix) helper that archives and moves the
  vector into the tier-2 index in one step. cleanup_orphan_vectors remains
  as the end-of-cycle safety net.
• Soft delete now moves the vector to the tier-2 index instead of
  leaving it in the active index (delete_memory(hard=False)); the move
  never blocks the archive itself.
• Hard delete purges tier-2 rows too. delete_memory(hard=True) used to
  stop at the active index, leaving embed_meta_arch/embed_vec_arch rows
  behind forever.
• Doctor: UTC embedded_at dialect detected and migrated. Tables whose DDL
  predates the localtime default are rebuilt with the canonical schema and
  existing values converted via datetime(x, 'localtime') (DST-correct,
  detected from sqlite_master so the check needs no marker and is
  idempotent). Pre-migration backup taken.
• Doctor: orphan tier-2 rows detected and cleaned (--migrate), plus
  advisory counts for archived memories without a vector and rows with
  legacy pre-canonical hashes, both pointing at reindex-archived.

Added

• reindex-archived re-embeds legacy-hash rows: tier-2 meta rows with a
  pre-v10.6 truncated (16-char) hash were embedded under a pre-canonical
  formula; they are re-embedded and re-hashed, reported as
  legacy_reembedded. Backfill of missing vectors unchanged and idempotent.
• embed_vec_arch is created with the declared-PK schema
  (vec0(id INTEGER PRIMARY KEY, ...)) on new stores, matching what the
  active side already handles; existing implicit-rowid arch tables keep
  working through a new _arch_join_col detection used by every arch-side
  query (store, search, move, cleanup, doctor). No rebuild of existing
  tables: both schemas are supported in the wild, same policy as embed_vec.
• Conn-level lifecycle helpers move_embedding_to_archive_conn /
  _store_archived_embedding_conn shared by the store methods, the
  consolidation phases and external plumbing.
• 9 new tests (273 total).