docs(research): add README describing research notes

Document what research notes are (opinionated investigations of a
question/design space), their unnumbered kebab-case naming, and their
loose verdict-first shape — explicitly freeform, not a template. Point
the AGENTS.md research line at it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/research/README.md

@@ -0,0 +1,42 @@
+# Research notes
+
+Investigations into a question or a design space — landscape surveys,
+tradeoff analyses, "should we do X or Y," assessments of an approach
+before (or instead of) committing it to a PRD. A research note is where
+the *thinking* lives; a PRD is where a decided feature lives, and a
+decision record is where a settled choice lives (see
+[`../README.md`](../README.md) for picking between them).
+
+Notes are opinionated. They reach a conclusion rather than dumping a
+neutral survey — the point is to move a decision forward and leave a
+durable record of why it went the way it did.
+
+## Naming
+
+`kebab-case-topic.md`, named by subject and **not** numbered (unlike
+PRDs and decision records). Pick a name that says what was
+investigated: `bash-vs-python-vs-go.md`, `pipelock-assessment.md`,
+`issue-tracking-vs-in-repo-decision-history.md`.
+
+## Shape (freeform)
+
+There's no fixed template — use whatever structure fits the question.
+In practice most notes share a loose shape:
+
+- **Open with the question** — a sentence or two on what's being
+  investigated and why it came up.
+- **Lead with the verdict** — a `## Summary` near the top stating the
+  conclusion, so a reader gets the answer without reading the whole
+  thing.
+- **Then the analysis** — whatever the argument needs: comparison
+  tables, per-option sections, failure-mode walkthroughs, the axes that
+  actually matter.
+- **End with a recommendation** when the note exists to drive a
+  decision.
+
+Keep the reasoning self-contained and grounded: cite sources, link
+files and PRDs, and prefer concrete evidence from this repo over
+generic claims — a note should stand on its own without a chat log or a
+forge thread. When a note's recommendation gets acted on, capture the
+resulting decision in a PRD or a decision record; the note stays as the
+"why we looked into it," not the system of record for the choice.