Add a Chinese README, and drop two references readers cannot follow

README.zh-CN.md is a full translation rather than a summary: the same 26
sections, the same code blocks. Both files link to each other.

The English README pointed readers at "the implementation plan" twice, for
a file that lives outside the repository. The README has since grown to
cover that design material itself, so the pointers went rather than the
content.

README.md

@@ -1,5 +1,7 @@
 # NexusTerm
 
+**English** · [中文](README.zh-CN.md)
+
 A desktop SSH session manager for Linux — connection tree, tabbed terminals,
 tunnels, local shell and serial.
 
@@ -9,7 +11,7 @@ OS keyring rather than a vendor's cloud.
 
 ## Status
 
-Early. See the milestone table in the implementation plan.
+Early. Everything below reflects what actually works today.
 
 | Milestone | Scope | State |
 |---|---|---|
@@ -472,6 +474,3 @@ previous schema intact rather than a half-converted database.
 `tests/migration002.test.ts` exercises this against a database built in the
 *old* shape and filled with old-format rows. Testing a migration against a fresh
 database would exercise none of its code paths.
-
-See the implementation plan for the full design, including the data model,
-flow-control protocol, and the packaging notes.