Complete bunx and current text-lockfile corpus compatibility

Tracks the next Bun corpus compatibility tranche from #66.\n\nScope:\n- Bun test API conditional modifiers on concurrent and serial runners\n- bunx package/version/bin selection and per-cache-root --no-install behavior\n- POSIX process identity methods used by bunx cache naming\n- refusal of symlinked or group/world-writable bunx cache roots with causal diagnostics\n- current v2 text lockfiles for catalogs and new projects while preserving existing v1 and flooring v0 to v1\n- JSONC-compatible re-read of emitted text lockfiles\n\nValidation target:\n- bunx.test.ts: 33 pass, 0 fail, 0 unsupported, 1 upstream todo\n- catalogs.test.ts: 6 pass, 0 fail, 0 unsupported, 0 todo\n- config-version.test.ts: 3 pass, 0 fail, 0 unsupported, 0 todo\n- lockfile-version-2.test.ts: 9 pass, 0 fail, 0 unsupported, 0 todo\n- full loopback-enabled home_test gate: exit 0\n\nParent: #66

Completed and published directly to main in 061e420 (feat(runtime): complete bunx and lockfile compatibility).\n\nValidation:\n- bunx.test.ts: 33 pass, 0 fail, 0 unsupported, 1 upstream todo\n- catalogs.test.ts: 6 pass, 0 fail, 0 unsupported, 0 todo\n- config-version.test.ts: 3 pass, 0 fail, 0 unsupported, 0 todo\n- lockfile-version-2.test.ts: 9 pass, 0 fail, 0 unsupported, 0 todo\n- Rechecked the remaining sorted install frontier through test-dev-peer-dependency-priority.test.ts; all exact-green\n- Full loopback-enabled home_test gate completed with exit 0\n\nThe tranche adds composed concurrent/serial conditional test modifiers, bunx package and cache lifecycle behavior, POSIX identity methods, unsafe cache-root refusal diagnostics, v2 new-lock emission with v1 preservation/v0 flooring, and JSONC-compatible lockfile re-read. Parent tracking remains #66.