feat(inventory): implement inter-project material transfer backend

- Add ProjectTransfer database model and migration
- Implement project transfer service with immediate stock deduction on creation
- Support 100% full delivery receipt logic across destination warehouses
- Enforce canonical_specs_hash matching for cross-project stock merge
- Add RBAC guards and status lock on received transfers (409 Conflict)
- Register API router for transfers with on-the-way integration

sql/migration.sql

@@ -551,6 +551,35 @@ CREATE TABLE standard_conversions (
     CONSTRAINT uq_standard_conversion UNIQUE (from_unit, to_unit)
 );
 
+-- Inter-project material transfers
+CREATE TABLE project_transfers (
+    id                  UUID            NOT NULL DEFAULT gen_random_uuid() PRIMARY KEY,
+    from_project_id     UUID            NOT NULL REFERENCES projects(id) ON DELETE RESTRICT,
+    from_warehouse_id   UUID            NOT NULL REFERENCES warehouses(id) ON DELETE RESTRICT,
+    to_project_id       UUID            NOT NULL REFERENCES projects(id) ON DELETE RESTRICT,
+    material_id         UUID            NOT NULL REFERENCES materials(id) ON DELETE RESTRICT,
+    brand_id            UUID            REFERENCES brands(id) ON DELETE SET NULL,
+    unit_id             INTEGER         NOT NULL REFERENCES units(id) ON DELETE RESTRICT,
+    quantity            NUMERIC(18,6)   NOT NULL CHECK (quantity > 0),
+    specs               JSONB           NOT NULL DEFAULT '{}'::jsonb,
+    specs_hash          TEXT            NOT NULL DEFAULT 'default',
+    note                TEXT,
+    status              TEXT            NOT NULL DEFAULT 'in_transit' CHECK (status IN ('in_transit', 'received', 'cancelled')),
+    out_transaction_id  UUID            REFERENCES inventory_transactions(id) ON DELETE SET NULL,
+    transfer_date       TIMESTAMPTZ     NOT NULL DEFAULT now(),
+    transferred_by      TEXT,
+    received_at         TIMESTAMPTZ,
+    received_by         TEXT,
+    to_warehouse_id     UUID            REFERENCES warehouses(id) ON DELETE SET NULL,
+    receipt_allocations JSONB,
+    created_at          TIMESTAMPTZ     NOT NULL DEFAULT now(),
+    updated_at          TIMESTAMPTZ     NOT NULL DEFAULT now()
+);
+
+CREATE INDEX idx_project_transfers_from ON project_transfers(from_project_id, status);
+CREATE INDEX idx_project_transfers_to ON project_transfers(to_project_id, status);
+
+
 -- ============================================================================
 -- UPDATED_AT TRIGGER (auto-set updated_at on row modification)
 -- ============================================================================
@@ -579,6 +608,10 @@ CREATE TRIGGER trg_quote_attachments_updated_at
     BEFORE UPDATE ON quote_attachments
     FOR EACH ROW EXECUTE FUNCTION set_updated_at();
 
+CREATE TRIGGER trg_project_transfers_updated_at
+    BEFORE UPDATE ON project_transfers
+    FOR EACH ROW EXECUTE FUNCTION set_updated_at();
+
 -- ============================================================================
 -- AUTOMATION TRIGGERS (v2.5 + v2.6)
 -- ============================================================================