refactor(license): extract cameleer-license-api module from server-core

Splits the pure license contract types (LicenseInfo, LicenseValidator,
LicenseState, LicenseStateMachine, LicenseLimits, DefaultTierLimits) into a
new cameleer-license-api module under package com.cameleer.license.

Why: cameleer-license-minter previously depended on cameleer-server-core for
these types, dragging cameleer-server-core + cameleer-common onto the
classpath of every minter consumer (notably cameleer-saas). The SaaS
management plane has no business carrying server-runtime types — it only
needs the license contract to mint and verify tokens.

After:
  cameleer-license-minter -> cameleer-license-api  (no server internals)
  cameleer-server-core    -> cameleer-license-api
  cameleer-saas           -> cameleer-license-minter -> cameleer-license-api

Verified: mvn -pl cameleer-license-minter dependency:tree shows the minter
no longer pulls cameleer-server-core or cameleer-common. Full reactor
verify (-DskipITs) green: 371 tests pass.

LicenseGate stays in server-core (server-runtime state holder, not contract).

Closes cameleer/cameleer-server#156

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cameleer-license-minter/pom.xml

@@ -17,7 +17,7 @@
     <dependencies>
         <dependency>
             <groupId>com.cameleer</groupId>
-            <artifactId>cameleer-server-core</artifactId>
+            <artifactId>cameleer-license-api</artifactId>
         </dependency>
         <dependency>
             <groupId>com.fasterxml.jackson.core</groupId>