feat(sdk): Multi-Projekt-Architektur — mehrere Projekte pro Tenant

Jeder Tenant kann jetzt mehrere Compliance-Projekte anlegen (z.B. verschiedene
Produkte, Tochterunternehmen). CompanyProfile ist pro Projekt kopierbar und
danach unabhaengig editierbar. Multi-Tab-Support via separater BroadcastChannel
und localStorage Keys pro Projekt.

- Migration 039: compliance_projects Tabelle, sdk_states.project_id
- Backend: FastAPI CRUD-Routes fuer Projekte mit Tenant-Isolation
- Frontend: ProjectSelector UI, SDKProvider mit projectId, URL ?project=
- State API: UPSERT auf (tenant_id, project_id) mit Abwaertskompatibilitaet
- Tests: pytest fuer Model-Validierung, Row-Konvertierung, Tenant-Isolation
- Docs: MKDocs Seite, CLAUDE.md, Backend README

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-compliance/migrations/039_compliance_projects.sql

@@ -0,0 +1,95 @@
+-- Migration 039: Multi-Projekt-Architektur
+-- Enables multiple compliance projects per tenant (Cloud-Ready Multi-Tenancy)
+--
+-- Changes:
+-- 1. New table compliance_projects (project metadata)
+-- 2. sdk_states: Drop UNIQUE(tenant_id), add project_id column with FK
+-- 3. Migrate existing data: Create default project for each existing sdk_states row
+
+-- =============================================================================
+-- 1. New table: compliance_projects
+-- =============================================================================
+
+CREATE TABLE IF NOT EXISTS compliance_projects (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id VARCHAR(255) NOT NULL,
+    name VARCHAR(500) NOT NULL,
+    description TEXT DEFAULT '',
+    customer_type VARCHAR(20) DEFAULT 'new',       -- 'new' | 'existing'
+    status VARCHAR(20) DEFAULT 'active',            -- 'active' | 'archived' | 'deleted'
+    project_version INTEGER DEFAULT 1,
+    completion_percentage INTEGER DEFAULT 0,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    archived_at TIMESTAMPTZ
+);
+
+CREATE INDEX IF NOT EXISTS idx_compliance_projects_tenant ON compliance_projects(tenant_id);
+CREATE INDEX IF NOT EXISTS idx_compliance_projects_status ON compliance_projects(tenant_id, status);
+
+-- =============================================================================
+-- 2. sdk_states: Add project_id, adjust constraints
+-- =============================================================================
+
+-- Drop the old UNIQUE constraint on tenant_id (allows multiple states per tenant)
+ALTER TABLE sdk_states DROP CONSTRAINT IF EXISTS sdk_states_tenant_id_key;
+
+-- Add project_id column (nullable initially for migration)
+ALTER TABLE sdk_states ADD COLUMN IF NOT EXISTS project_id UUID;
+
+-- =============================================================================
+-- 3. Data migration: Create default projects for existing states
+-- =============================================================================
+
+-- For each existing sdk_states row without a project, create a default project
+INSERT INTO compliance_projects (id, tenant_id, name, customer_type, status)
+SELECT
+    gen_random_uuid(),
+    s.tenant_id,
+    COALESCE(s.state->'companyProfile'->>'companyName', 'Projekt 1'),
+    COALESCE(s.state->>'customerType', 'new'),
+    'active'
+FROM sdk_states s
+WHERE s.project_id IS NULL
+ON CONFLICT DO NOTHING;
+
+-- Link existing states to their newly created projects
+UPDATE sdk_states s
+SET project_id = p.id
+FROM compliance_projects p
+WHERE s.tenant_id = p.tenant_id AND s.project_id IS NULL;
+
+-- =============================================================================
+-- 4. Add constraints after migration
+-- =============================================================================
+
+-- Make project_id NOT NULL now that all rows have a value
+-- (Only if there are no NULL values remaining — safe guard)
+DO $$
+BEGIN
+    IF NOT EXISTS (SELECT 1 FROM sdk_states WHERE project_id IS NULL) THEN
+        ALTER TABLE sdk_states ALTER COLUMN project_id SET NOT NULL;
+    END IF;
+END $$;
+
+-- Unique constraint: one state per (tenant, project)
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_constraint WHERE conname = 'uq_sdk_states_tenant_project'
+    ) THEN
+        ALTER TABLE sdk_states ADD CONSTRAINT uq_sdk_states_tenant_project
+            UNIQUE (tenant_id, project_id);
+    END IF;
+END $$;
+
+-- Foreign key to compliance_projects
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_constraint WHERE conname = 'fk_sdk_states_project'
+    ) THEN
+        ALTER TABLE sdk_states ADD CONSTRAINT fk_sdk_states_project
+            FOREIGN KEY (project_id) REFERENCES compliance_projects(id) ON DELETE CASCADE;
+    END IF;
+END $$;