docs: document graphify workflow

Add repository guidance for using the local graphify knowledge graph when answering codebase questions.

Ignore local .codex and graphify-out artifacts so generated graph data and local skill files stay out of future commits.

Author: leandromqrs

.gitignore

@@ -5,3 +5,5 @@
 builddir/
 dist/
 crates/aetheris-app/libs/
+.codex/
+graphify-out/

AGENTS.md

@@ -136,3 +136,16 @@ Before finishing a change, check:
 - warnings are not introduced;
 - user-facing strings are concise and GNOME-style;
 - docs and workflows describe behavior that is actually implemented.
+
+## graphify
+
+This project has a knowledge graph at graphify-out/ with god nodes, community structure, and cross-file relationships.
+
+When the user types `/graphify`, use the installed graphify skill or instructions before doing anything else.
+
+Rules:
+- For codebase questions, first run `graphify query "<question>"` when graphify-out/graph.json exists. Use `graphify path "<A>" "<B>"` for relationships and `graphify explain "<concept>"` for focused concepts. These return a scoped subgraph, usually much smaller than GRAPH_REPORT.md or raw grep output.
+- Dirty graphify-out/ files are expected after hooks or incremental updates; dirty graph files are not a reason to skip graphify. Only skip graphify if the task is about stale or incorrect graph output, or the user explicitly says not to use it.
+- If graphify-out/wiki/index.md exists, use it for broad navigation instead of raw source browsing.
+- Read graphify-out/GRAPH_REPORT.md only for broad architecture review or when query/path/explain do not surface enough context.
+- After modifying code, run `graphify update .` to keep the graph current (AST-only, no API cost).