feat(console): per-tenant ledger read scoping (RBAC + tenant_id column)

[New1Direction]

Completes the authorization half of the console finding. Stacked on #3 (which closed the unauthenticated-access hole); base is fix/critical-security-3.

What this adds

• auth_guard.tenant_scope — derives the ledger read filter from the authenticated principal:
  • admin role (and the explicit dev opt-out) → read across all tenants;
  • any other principal → restricted to its own tenant_id;
  • authenticated but no tenant_id claim → 403 (can't be scoped safely).
• ledger_router — /traces, /trace/{id}, /summary now filter by the caller's tenant. One tenant can no longer see another's traces (a cross-tenant id resolves to 404).
• Schema — ExecutionTrace gains tenant_id (default "default"); StateLedger persists it and migrates legacy DBs in place (ALTER TABLE ADD COLUMN). It is metadata only — excluded from the content-addressed state hash, so determinism is unaffected.

Verification

• Full CI Python suite: 1263 passed, 0 failed
• New tests (TDD, RED→GREEN): test_ledger_tenant_scope.py (read isolation: own-tenant only / cross-tenant 404 / admin sees all / no-tenant 403) + test_ledger_tenant.py (persist + legacy migration + default).
• ruff check + format --check: clean.

Honest follow-up (not in this PR)

The orchestrator write-path is tenant-blind — it has no request context, so traces it writes persist as tenant_id = "default". Read-side isolation is fully enforced here; threading the real request tenant into those writes is a separate change (needs tenant context plumbed through the execution path).

🤖 Generated with Claude Code

[New1Direction]

Consolidated. All commits from this PR are now in rust-core-loadbearing (fast-forwarded through the full stack), together with the 17 previously-uncommitted source files the package needed to import. The integration branch now imports cleanly, the committed test suite passes, and ruff/mypy/parse gates are green on a fresh checkout. Closing as superseded — history is preserved on rust-core-loadbearing.