chore: initialize project docs

.project-docs/10-decisions/adr-template.md

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+# ADR-{number}: {decision title}
+
+## Status
+
+Proposed
+
+## Date
+
+{YYYY-MM-DD}
+
+## Context
+
+{context that made the decision necessary}
+
+## Decision
+
+{decision made}
+
+## Rationale
+
+{why this option was chosen}
+
+## Consequences
+
+- {positive or negative consequence}
+
+## Supersedes
+
+- {older ADR or decision, if any}
+
+## Related
+
+- {related doc or source file}

.project-docs/10-decisions/decision-index.md

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+# Decision Index
+
+## Active Decisions
+
+| ID | Decision | Status | Date | Applies To | Detail |
+|---|---|---|---|---|---|
+
+## Superseded Decisions
+
+| ID | Decision | Superseded By | Date |
+|---|---|---|---|
+
+## Decision Criteria
+
+Create or update an ADR when a choice affects:
+
+- project positioning
+- architecture boundaries
+- public behavior
+- data model
+- long-term maintenance
+- user-facing workflow