Add BOC-aware lock detection and E1C-aided tracking

docs/e1_pilot_aided_tracking.md

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+# E1C-pilot-aided E1B tracking
+
+The default E1 architecture uses two phase-coherent correlator branches:
+
+```text
+raw SignalSim IQ8
+  -> E1C PCPS acquisition
+  -> E1C 25-symbol secondary-code phase/frequency search
+  -> shared double-precision carrier and code phase vectors
+       -> E1C VE/E/P/L/VL -> FLL/PLL/DLL/CN0/BOC lock
+       -> E1B VE/E/P/L/VL -> 4 ms Prompt stream -> I/NAV decoder
+```
+
+The secondary synchronizer jointly searches code phase and residual carrier
+frequency using complex 4 ms Prompt values. Its estimated secondary phase is
+then applied at every E1C primary-code epoch. Integrations may divide the 4 ms
+primary period exactly; the 2 ms navigation configuration applies the same
+secondary symbol to both halves.
+
+E1B navigation polarity never enters the pilot loop discriminators, C/N0
+estimator, or lock detector. The E1B branch receives the identical carrier and
+code phase arrays before either NCO advances, preserving sample-by-sample
+coherence. Only E1B Prompt I/Q is passed to symbol synchronization and I/NAV
+decoding.
+
+The initial 400 ms E1C secondary search operates on a buffered portion of the
+same input stream. The offline regression replays that buffer through the
+closed loops after synchronization; it does not load frozen Prompt, symbol,
+page, or ephemeris artifacts. A streaming implementation can use the same
+bounded input buffer or start output after synchronization.
+
+This pilot architecture is a separate robustness improvement. It is not used
+to conceal the legacy BOC metric defect: E1B-only and E1C-aided modes are both
+evaluated with the same corrected BOC-aware lock detector.