feat: add full test suite (C + JS) and test-suite.yml CI workflow

[Copilot]

No real tests existed — npm test was a no-op echo and CMake had only a smoke-run of the binary.

Test suite (tests/)

• test_simsim.c — build sanity + exit-code contract (4 assertions)
• test_maxopts.c — 9 unit tests for maxopts_everything_this_era(): nominal paths, NULL, zero/negative size, INT_MAX boundary
• test_index.js — 15 tests for index.js: module shape, init()/info() return values, link format, idempotency

Build wiring

• CMakeLists.txt: adds test_simsim and test_maxopts executables as UnitTest_* CTest targets
• package.json: test script now runs node tests/test_index.js

Workflow (.github/workflows/test-suite.yml)

• Triggers: push/PR to prod/main/production + workflow_dispatch
• Jobs: JS tests (Node 18/20/22), CMake build+ctest (gcc + clang), direct C compile+run (gcc + clang), summary gate
• All jobs scoped to permissions: contents: read

[Copilot]

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