Close SUM-PLAT-18: currency rates and UoM platform models

[jay009id]

Closes #57

Summary

Platform primitives for transactional verticals (SUM-PLAT-18): transactional apps need FX and unit-of-measure support before they ship, and the currency model was catalog-only with no rates while UoM models did not exist at all.

• core.currency.rate — per-currency rates effective from a date (currency_id, rate, date_from, active), with a (currency, date_from) natural key for idempotent data syncs. The core.currency catalog moves from addons/geo to addons/base (a single reference in the whole repo, no existing data → no migration), so catalog + rates + UoM ship as one always-on platform unit.
• uom.category + uom.uom — units of measure with a factor relative to the reference unit of their category and a rounding precision, natural key (name, category).
• Conversion helpers — sdk.ConvertCurrency, sdk.ConvertUom, and sdk.ConvertMoneyField (resolves the currency=<field> tag from the model registry — a tag that was parsed but never consumed before). Helpers use the newest rate with date_from <= the conversion date; cross-category UoM conversions are rejected explicitly.
• Admin views in addons/base only (no accounting app) — a "Currencies & Units" menu (currencies, rates, UoM categories, units), 8 list/form views, 4 window actions, seed data: 8 currencies with bootstrap rates (USD reference 1.0), 5 UoM categories, 16 units.

Checklist

• make from sumeru/ (lint, test, build) — full gate green, golangci-lint 0 issues, coverage 42.5% (min 42)
• Sensitive fields → core/security/fields.go; bypass → AuditedBypass / WithElevated — no new sensitive fields; helpers act in the caller's context, no new bypass paths
• Auth/session cookies → core/server/web/cookie_helpers.go — no cookie/auth changes
• Tests under test/ or core/swc/tests/ where behavior changed — unit, addon, and integration tests added; no SWC changes

If applicable: make generate — ran, output committed · make test-modules — green · make test-integration — green against local PostgreSQL

Notes

• Pre-existing first-time install bug (follow-up needed): install base failed: en_US.po: relation "sys_translation" does not exist — PO import runs before the sys_translation table (owned by the i18n addon) is created. Reproduced identically on dev; deserves its own issue.
• make test-integration did not build on dev (orm.InitDB used as a value in test/module/integration/install_closure_test.go); the second commit of this PR fixes that and adds bypass contexts to both integration smoke tests.
• Rates are global in this first iteration; verticals can layer company-scoped rates and rate providers on top.
• Two workspace tests (TestWorkspaceAddonsPathOptional, TestRunWorkspaceGen_scopedWrites) used to fail on the dev machine due to the external sumeru_addons workspace (stock-orig folder) — fixed separately and now passing; unrelated to this PR.