docs: polish Indexical Circuits for research portfolio

[Rinetta1981]

Summary

Polishes Indexical Circuits as a completed research artifact without
changing any experimental results.

This update:

• restructures the README around the replication sequence and evidence gate;
• surfaces the primary null results and secondary truth-dependent finding;
• makes the closed mechanistic gate explicit;
• adds a lightweight reproducibility guide;
• adds a minimal dependency manifest for repository tests;
• adds GitHub Actions CI for automated integrity checks;
• preserves the distinction between exploratory and confirmatory stages.

Scientific status

The completed evidence sequence remains unchanged.

The original generic-formality hypothesis did not replicate.

The held-out role-relational hypothesis did not replicate.

The preregistered focused functions as primary hypothesis did not
replicate.

A secondary truth-dependent interaction was observed but is retained as a
hypothesis-generating result requiring independent replication.

Because the pre-specified behavioral criterion was not met, mechanistic
localization was intentionally not pursued.

No causal "authority circuit", "indexical circuit", or equivalent mechanism
is claimed.

Reproducibility

The repository now includes lightweight automated CI while preserving the
original GPU/model experiments in their chronological notebooks.

CI is green.