docs: migrate README.md / README.zh_CN.md to a single NRG template

[andriishin]

Why

README.md and README.zh_CN.md are hand-maintained side-by-side. Every README change means editing the same paragraph in two places.

This PR migrates both files to a single source-of-truth template using Nanolaba Readme Generator (NRG) — a small Java 8 Maven plugin that turns one README.src.md into N localized README files on every build.

What changes

• New: README.src.md — the unified source. Each line is tagged <!--en--> or <!--zh_CN-->. Generated programmatically; outputs are byte-identical to today's files (modulo a 2-line auto-generated header).
• Modified: pom.xml — adds com.nanolaba:nrg-maven-plugin:1.1 to the parent POM's <build><plugins> after maven-compiler-plugin with <inherited>false</inherited>. Bound to the compile phase.
• Modified: README.md (+2 lines), README.zh_CN.md (+2 lines) — regenerated. The only change is the 2-line auto-generated header at the top.

Verification

Locally, regenerating with NRG 1.1 from Maven Central against current master produces output that diffs against the originals only by the 2-line auto-generated header. Zero functional content change.

How to regenerate locally

mvn compile

About NRG

com.nanolaba:readme-generator — open-source, Apache 2.0, Java 8+. Ships as CLI, Maven plugin, GitHub Action, and library.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.83954%. Comparing base (953a3c6) to head (cad834d).

Additional details and impacted files

@@                  Coverage Diff                  @@
##                master        #139         +/-   ##
=====================================================
- Coverage     85.86041%   85.83954%   -0.02088%     
+ Complexity        4325        4318          -7     
=====================================================
  Files              436         436                 
  Lines            14371       14371                 
  Branches          1286        1286                 
=====================================================
- Hits             12339       12336          -3     
- Misses            2032        2035          +3     

see 1 file with indirect coverage changes

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[andriishin]

Closing this — the Tencent CLA requirement is broader than I want to commit to in exchange for a docs-only contribution. If a maintainer would like the NRG migration applied internally without going through the CLA path, the template and pom snippet are at https://github.com/andriishin/trpc-java/tree/nrg-migration. Thanks!