Initial Galileo receiver and SignalSim integration

docs/configuration.md

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+# Configuration
+
+`ReceiverConfig` owns RF, acquisition, tracking, front-end, and fixed-point
+dataclasses. YAML loading is strict: a misspelled field is an error.
+
+Important validation rules include positive sampling/loop rates, a real IF
+strictly below Nyquist, integer sample counts per integration interval,
+ordered correlator tap spacing, explicit FFT length when requested, E1B
+bit-transition protection beyond 4 ms, and E1C secondary-code handling beyond
+4 ms. E1B tracking is conservatively limited to 4 ms until navigation-symbol
+synchronization is implemented.
+
+`intermediate_frequency_hz` may be nonzero for either real or analytic input.
+The front end always outputs complex baseband and divides the effective sample
+rate by the integer decimation factor. Acquisition/tracking must use that output
+rate.
+
+Acquisition parallelism fields expose future hardware/software scheduling but
+do not change numerical results. `zero_padding_mode: none` provides the exact
+N-sample circular correlation. A longer FFT changes the sampled numerical
+correlation/edge convention; it is not additional physical delay information.
+
+Default YAML files:
+
+- `e1_default.yaml`: requested 16.368 MHz nominal defaults.
+- `acquisition_example.yaml`: faster 4.092 MHz executable search.
+- `tracking_example.yaml`: 4.092 MHz tracking defaults.
+