docs(adr): add ADRs 006-009 for vertical refactor

docs/decisions/adr-008-per-feature-di-containers.md

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+# ADR-008: Per-Feature InversifyJS Containers
+
+**Status:** Accepted
+**Date:** 2026-05-04
+
+## Context
+
+The original template used a single shared InversifyJS Container in `packages/core/src/di/`. As the number of features grows, the container becomes a point of coordination: adding a symbol requires modifying shared code, and tests that mock one feature risk breaking others.
+
+## Decision
+
+Each feature owns its own `Container` and symbol table. No shared DI state. Tests rebind per feature in isolation. Apps boot by calling `bindProduction*()` for each feature independently.
+
+**Example:**
+```typescript
+// packages/blog/src/di/container.ts
+export const container = createContainer();
+
+// packages/blog/tests/feature.test.ts
+beforeEach(() => {
+  rebindRepository(new TestRepository());
+  // Only blog's container is affected
+});
+```
+
+## Consequences
+
+- Zero cross-feature DI coupling — each feature's test can mock its repos without coordination
+- Symbol collisions impossible — each feature has its own `ARTICLES_REPOSITORY` symbol
+- Shared services (if needed) are explicitly bound in each feature that uses them
+- Apps must boot each feature's container on startup
+
+## Alternatives Considered
+
+- Single shared container: Simpler upfront, becomes a bottleneck and test coordination point
+- Function injection (no DI): Avoids framework overhead, but loses the scaling benefits of DI