fix(migration): swap obsolete --primary/--fallback for --backend in L3 scripts

[DarkCodePE]

Summary

ruflo >=3.7.0-alpha.67 collapsed the old --primary <backend> --fallback <backend> flag pair into a single --backend <backend> flag (verify with ruflo memory configure --help). The L3 migration and rollback scripts still called the old form, which the new CLI silently ignores — so step 7 (cutover) and rollback step 2 became no-ops while the scripts reported SUCCESS.

Why this matters

Per the L3 runbook (MIGRATION-PG.md step 7), cutover is what actually flips the repo from sql.js to RuVector. With the stale flag, the migration would complete, the new schema would be populated, but ruflo memory store/search would keep hitting .swarm/memory.db. The rollback path had the symmetric bug.

Discovered during a real migration attempt this turn: ruflo memory configure --primary ruvector --fallback sqljs returned no error but did nothing.

Changes

File	Step	Before	After
scripts/migrate-l2-to-l3.sh	7 (cutover)	--primary ruvector --fallback sqljs	--backend ruvector
scripts/rollback-l3.sh	2 (revert)	--primary sqljs --fallback none	--backend sqljs
docs/arquetipo/deliverables/memory/MIGRATION-PG.md	§7	same swap	same swap

A short comment near each call explains the flag collapse so future readers don't reintroduce the old form.

Out of scope

Five additional references to the obsolete flags live in historical research/design docs under docs/arquetipo/sprint5/ and docs/arquetipo/research/. Per surgical-changes rule, those are point-in-time records from sprint 5 and were not touched:

• docs/arquetipo/research/b10-memory-strategy.md:362
• docs/arquetipo/sprint5/architecture-design.md:310, 334
• docs/arquetipo/sprint5/research-findings.md:464, 491

If we want a clean sweep, that's a separate doc-archive PR.

Behavior change to acknowledge

The new --backend flag has no "fallback" concept; fallback selection is now runtime-implicit. The runbook line was updated to reflect this. If a teammate relied on the explicit dual-backend chain, this is the moment to surface that.

Test plan

• bash -n scripts/migrate-l2-to-l3.sh passes.
• bash -n scripts/rollback-l3.sh passes.
• bash scripts/migrate-l2-to-l3.sh --dry-run shows the new command: [dry-run] ruflo memory configure --backend ruvector.
• Real migration end-to-end against a populated .swarm/memory.db and a healthy ruvector-postgres container (deferred to follow-up turn; container is up and healthy, schema claude_flow.embeddings still pending creation).

Co-Authored-By: claude-flow ruv@ruv.net