Rename neural experiments to descriptive paths (drop N* codes)

configs/neural/{N0,N1,N2,N5}.yaml -> {bridge,collapse,grounding,architectures}.yaml,
results dirs likewise. Updated experiment/output.dir fields, comments/docstrings, and
docs; regenerated the four result manifests (now carrying the real git commit). No
functional path resolution referenced the codes (the Makefile globs configs/neural/*.yaml
and tests use inline configs), so nothing breaks. 92 tests green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

configs/neural/N0.yaml

@@ -1,42 +0,0 @@
-experiment: N0_bridge_histogram
-kind: gen_lineage
-seed: 20260704
-n_replicates: 60
-generations: 200
-
-# Bridge / harness-faithfulness check (Layer 1.5 build-order Stage B): run the E2 grounding
-# phase-boundary sweep through the NEURAL runner with the histogram model, which is exactly
-# neutral Wright-Fisher drift with immigration. Stationary H must track the closed form
-# H_eq = H* * m(2n+m-1)/(n+2nm+m^2) and reproduce a critical g* << 1 — i.e. the neural
-# plumbing reproduces the analytic core before any real network is trained. R=1 so every
-# grounding policy reduces to the proportional immigration model H_eq is derived for.
-synthetic:
-  K: 200
-  R: 1
-  tail: zipf
-  zipf_s: 1.1
-  tail_frac: 0.5
-  tail_threshold: 1.0e-3
-  init: truth
-  style_len: 2
-  style_vocab: 4
-  id_base: 2
-
-model:
-  kind: histogram
-
-dynamics:
-  n: 200
-  grounding: {m: 0, policy: proportional}   # m is overwritten per g by the sweep
-  remint: {enabled: false, period: null, H_gate: null}
-
-metrics:
-  kl_floor: 1.0e-9
-  support_eps: 1.0e-9
-
-sweep:
-  - param: g
-    values: [0.0, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.4]
-
-output:
-  dir: results/N0