research/: add a README index; revise topic files instead of adding dated run records #279

If we do it: a reader who never saw the issue can find what link has settled from one index, and future parity runs revise one topic file instead of adding a dated sibling. If we never do: the largest research/ in the fleet (26 files) stays discoverable only through eight path citations in CLAUDE.md, and each provincial run adds another file that duplicates its own PWF archive.

Problem

research/ holds 26 files and no README.md; README.md at the repo root never mentions the directory. Measured 2026-09-06:

• roughly two-thirds are point-in-time run records — provincial_parity_2026_05_01/_11/_12/_25.md, parity_accessible_habitat_2026_07_03.md, run_record_2026_08_31_cypher_pilots.md, distributed_2hosts_2026_05_01.md — each opening with Run / Hardware / Software / Configuration blocks and each with one revision
• one-third are living documents — bcfishpass_methodology.md (3 revisions), study_area_run.md (8), provincial_run_runbook.md (3), the bcfp_* reference files — which is the shape that moves the state of knowledge
• three filename patterns coexist: topic.md, topic_YYYY_MM_DD.md, and run_record_YYYY_MM_DD_x.md

The soul convention now says: one topic file revised in place, git as the version record, run records in the PWF archive README plus committed logs, and a README index with a naming cutover line — conventions/planning.md, "research/ — what is known, outliving the issue that found it" (NewGraphEnvironment/soul#202).

Proposed solution

1. Add research/README.md: one row per file with what it covers (rfp's is the model), a "Related work" list (fresh, bcfishpass, db_newgraph), and the cutover line:

   Naming: `<topic>.md`, revised in place, from 2026-09-06.
   Files dated before that carry a `_YYYY_MM_DD` suffix; they are not being renamed.
   

2. Do not rename anything — CLAUDE.md, PR bodies and issues cite these paths.

3. Going forward, a provincial parity run revises provincial_parity.md (create it from the 2026-05-25 state, header naming the archive and log prefix that last moved it) rather than adding provincial_parity_<date>.md; the run record itself goes in that issue's planning/archive/<issue>/README.md Measurement / Evidence sections.

4. CLAUDE.md links the README once; keep the individual citations only where a rule depends on the file (bcfp_divergence_taxonomy.yml read by lnk_parity_annotate() is one).

Relates to NewGraphEnvironment/soul#202