docs: migrate Obsidian vault

docs/AGENTS.md

@@ -0,0 +1,35 @@
+# Brain Agent Instructions
+
+This repository is an Obsidian vault for an execution-focused second brain.
+
+## Vault structure
+
+- `00 INBOX/` is the trusted capture point for unprocessed or intentionally pending items.
+- `00 INBOX/ai/` is the AI boundary and default scratch area for AI-generated work.
+- `01 sources/` is for ingested external sources.
+- `02 notes/` is for reviewed notes that are not source notes and not active work state.
+- `03 wrk/` is for active execution state and workstream notes.
+- `99 meta/` is for vault infrastructure such as templates, attachments, and Obsidian support files.
+
+## AI boundary
+
+AI may freely create and edit files inside `00 INBOX/ai/`.
+Creating or editing files elsewhere requires explicit user approval, unless the user explicitly requested that specific file change.
+AI-generated material outside the boundary is provisional until reviewed or explicitly promoted.
+
+## Working style
+
+Prefer one file per capture.
+Do not create rolling capture notes unless the user explicitly asks for one.
+Keep folders flat unless real navigation pain justifies grouping.
+Do not create tags, tag notes, maps, or indexes before they earn their place.
+Treat source ingestion as mechanical work that still needs human review at some point.
+Prefer positive agent instructions that describe what to do.
+Include negative decisions only when they prevent a likely, harmful, or repeated mistake.
+
+## Templates
+
+Remove template instruction text when writing a note from a template.
+
+## Gotchas
+