chore: add project documentation framework

.project-docs/05-agent-entry/memory-index.md

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+# Memory Index
+
+Use this as the high-density entry point after the Concurrent Task Gate establishes task identity and worktree ownership.
+
+## Startup Set
+
+- Active task: `.project-docs/30-worklog/tasks/{task_id}.md`
+- Project identity: `.project-docs/00-brief/project-positioning.md`
+- Integrated state: `.project-docs/30-worklog/current-state.md`
+- Decision list: `.project-docs/10-decisions/decision-index.md`
+- System shape: `.project-docs/20-architecture/system-overview.md`
+
+## Recall Pointers
+
+- Evidence-heavy bugs, experiments, investigations: `.project-docs/50-evidence/evidence-index.md`
+- Workflow lessons and repeated agent mistakes: `.project-docs/60-reflection/reflection-index.md`
+- Pending promises, loops, timed follow-ups: `.project-docs/80-commitments/commitments.md`
+- Integrated stale items: `.project-docs/90-maintenance/stale-items.md`
+- Task-scoped conflicts: `.project-docs/90-maintenance/conflicts/{task_id}__<slug>.md`
+
+## Loading Rule
+
+Keep this file short. Add shared pointers only during Integration Gate. Feature tasks keep their working context and promotion candidates in their own task record.