Numerical-hygiene pass on the solver crate for the pre-publication review — closes the last correctness-adjacent items from the review checklist (fast-grid dedup + the two biexp TODOs) and removes remaining bare-literal / duplicated tuning constants per the no-magic-numbers rule. No behavior change: every default reproduces the previously hardcoded value.

Biexp fast-grid dedup (biexp_fit.rs)

• Hoist the fast-component grid bounds (0.25/2.0/0.5/8.0 × dt, 0.15 × tau_d) into shared named consts (TRF_*/TDF_*), used by both cold_grid_search and golden_section_refine so the two stages can no longer drift apart.
• Fixes a real drift: refinement floored tau_r_fast at 0.1 × dt while the grid floored at 0.25 × dt, letting refinement explore a region the grid never searched. Refinement now clamps to the same shared bounds (and the tau_d_fast refine floor is clamped to the grid floor too).
• Resolve the two long-standing TODOs (sequential ceiling necessity; dt-relative vs fixed-ms bounds) as documented design decisions with rationale, rather than open markers.

Seed / baseline / EMA config-ification

• Introduce SeedConfig (mad_multiplier, onset_fraction, max_walkback_s, min_peak_distance_s) with Default; find_seed_spikes reads from it instead of bare literals (4.0, 0.10, 1.0, 5.0). FFI binding signatures (seed_trace, seed_kernel_estimate) are unchanged.
• Home the rolling-baseline percentile as baseline::DEFAULT_BASELINE_QUANTILE, used by both Solver::subtract_baseline and indeca::solve_trace — previously the literal 0.2 was duplicated across two modules (a drift hazard like the fast-grid one).
• Name the display-only baseline EMA weight as BASELINE_EMA_WEIGHT.

Testing

• 131 Rust tests pass; 207 Python tests pass (2 skipped).
• clippy clean under both --features jsbindings and --features pybindings.
• cargo fmt --all --check clean.

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