feat: add cameleer-license-minter dependency and V002 migration

Adds Ed25519 license minting library, signing_keys table,
renames tiers (LOW→STARTER, MID→TEAM, HIGH→BUSINESS, BUSINESS→ENTERPRISE),
adds label + grace_period_days to licenses, drops features column.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/main/resources/db/migration/V002__license_minter.sql

@@ -0,0 +1,34 @@
+-- V002: License minter integration
+-- Ed25519 signing keys for license minting
+CREATE TABLE signing_keys (
+    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    public_key_b64  TEXT NOT NULL,
+    private_key_b64 TEXT NOT NULL,
+    active          BOOLEAN NOT NULL DEFAULT TRUE,
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Rename tiers: LOW→STARTER, MID→TEAM, HIGH→BUSINESS, BUSINESS→ENTERPRISE
+-- Single CASE pass to avoid double-rename
+UPDATE tenants SET tier = CASE tier
+    WHEN 'LOW' THEN 'STARTER'
+    WHEN 'MID' THEN 'TEAM'
+    WHEN 'HIGH' THEN 'BUSINESS'
+    WHEN 'BUSINESS' THEN 'ENTERPRISE'
+    ELSE tier
+END WHERE tier IN ('LOW', 'MID', 'HIGH', 'BUSINESS');
+
+UPDATE licenses SET tier = CASE tier
+    WHEN 'LOW' THEN 'STARTER'
+    WHEN 'MID' THEN 'TEAM'
+    WHEN 'HIGH' THEN 'BUSINESS'
+    WHEN 'BUSINESS' THEN 'ENTERPRISE'
+    ELSE tier
+END WHERE tier IN ('LOW', 'MID', 'HIGH', 'BUSINESS');
+
+-- Add new license columns for Ed25519 model
+ALTER TABLE licenses ADD COLUMN label VARCHAR(255);
+ALTER TABLE licenses ADD COLUMN grace_period_days INTEGER NOT NULL DEFAULT 0;
+
+-- Drop features column (server enforces caps, not feature flags)
+ALTER TABLE licenses DROP COLUMN features;