chore: prepare v1.9.0 release (#666)

- Bump version to 1.9.0 in package.json, package-lock.json, .opencode/package.json
- Add v1.9.0 changelog with 212 commits covering selective install architecture,
  6 new agents, 15+ new skills, session/state infrastructure, observer fixes,
  12 language ecosystems, and community contributions
- Update README with v1.9.0 release notes and complete agents tree (27 agents)
- Add pytorch-build-resolver to AGENTS.md agent table
- Update documentation counts to 27 agents, 109 skills, 57 commands
- Update version references in zh-CN README
- All 1421 tests passing, catalog counts verified

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "ecc-universal",
-  "version": "1.8.0",
+  "version": "1.9.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "ecc-universal",
-      "version": "1.8.0",
+      "version": "1.9.0",
       "hasInstallScript": true,
       "license": "MIT",
       "dependencies": {