[liulimengmeng-cmd]

What changed

• add the Zhang hybrid PPP-RTK service and user product-relation pipeline
• add integer-estimable product-basis, gauge, WL/L1 conditioning, PAR, NIS, temporal/BESD, and checkpoint components
• integrate the pipeline into PEA configuration, ambiguity resolution, product generation, and user-product loading
• add Zhang full-rank and checkpoint unit-test coverage
• accept the 49-column extended Zhang product format in the user adapter

Why

The existing implementation did not provide a closed service-to-user integer-product path. In particular, the product-relation lattice, cross-frequency WL/L1 covariance conditioning, persistent gauge transport, and user-side product parsing needed explicit implementation and validation hooks.

Current validation boundary

• git diff --cached --check passed before commit.
• The 2024/199 five-user adapter-fix v3 campaign completed all 30 cases with the expected 32 full-window and 11 restart epochs.
• The products are loaded and produce non-zero user WL candidates, but the current scientific result is not a successful PPP-AR solution: conditional L1 passed 0 epochs, newly_fixed_total=0, and AR coordinates remained identical to FLOAT.
• A fresh unit-test execution was not available at publication time because the expected zhang_full_rank_tests executable was not present in the current WSL build tree. This PR must not be treated as final scientific acceptance.

Excluded intentionally

Experiment outputs, ZIP archives, logs, binaries, temporary directories, bulk run configurations, and generated version headers were not committed.