Prepare SDK Tier 2 assessment submission

- Add CHANGELOG.md with release lines and history
- Refresh ROADMAP.md: 2.x stable line, 3.0.x for 2026-07-28 spec (first
  milestones Sep 2026), Tier 2 commitment, 1.x/0.x security-patches-only
- Refresh VALIDATION_RESULTS.md: 2026-08-17 run on conformance suite
  0.2.0-alpha.11 (server 73/73, auth 193/193, client 3/4 w/ sse-retry baselined)
- Bump conformance CI action pins v0.1.11 -> v0.1.16
- Update docs with missing features

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

.github/workflows/conformance.yml

@@ -27,7 +27,7 @@ jobs:
           timeout 30 bash -c 'until curl -s http://localhost:8080/mcp > /dev/null 2>&1; do sleep 0.5; done'
 
       - name: Run conformance tests
-        uses: modelcontextprotocol/conformance@v0.1.11
+        uses: modelcontextprotocol/conformance@v0.1.16
         with:
           mode: server
           url: http://localhost:8080/mcp
@@ -54,7 +54,7 @@ jobs:
         run: mvn clean install -DskipTests
 
       - name: Run conformance test
-        uses: modelcontextprotocol/conformance@v0.1.11
+        uses: modelcontextprotocol/conformance@v0.1.16
         with:
           mode: client
           command: 'java -jar conformance-tests/client-jdk-http-client/target/client-jdk-http-client-*-SNAPSHOT.jar'