docs: add Trellis planning and project specs

.trellis/spec/shared/index.md

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+# Shared Development Guidelines
+
+> These guidelines apply to all Next.js full-stack applications using this architecture.
+
+---
+
+## Documentation Files
+
+| File                                   | Description                          | When to Read            |
+| -------------------------------------- | ------------------------------------ | ----------------------- |
+| [code-quality.md](./code-quality.md)   | Code quality mandatory rules         | Always                  |
+| [typescript.md](./typescript.md)       | TypeScript best practices            | Type-related decisions  |
+| [dependencies.md](./dependencies.md)   | Dependency versions and constraints  | Adding/updating deps    |
+
+---
+
+## Quick Navigation
+
+| Task                        | File                                   |
+| --------------------------- | -------------------------------------- |
+| Code quality rules          | [code-quality.md](./code-quality.md)   |
+| Type annotations            | [typescript.md](./typescript.md)       |
+| Dependency management       | [dependencies.md](./dependencies.md)   |
+
+---
+
+## Core Rules (MANDATORY)
+
+| Rule                                      | File                                   |
+| ----------------------------------------- | -------------------------------------- |
+| No non-null assertions (`!`)              | [code-quality.md](./code-quality.md)   |
+| No `any` type                             | [code-quality.md](./code-quality.md)   |
+| No `@ts-expect-error` / `@ts-ignore`      | [code-quality.md](./code-quality.md)   |
+| No `console.log` (use structured logging) | [code-quality.md](./code-quality.md)   |
+| Zod-first type definitions                | [typescript.md](./typescript.md)       |
+| Import types from backend, never redefine | [typescript.md](./typescript.md)       |
+| Standard response format (`success` + `reason`) | [typescript.md](./typescript.md) |
+
+---
+
+## Before Every Commit
+
+- [ ] `pnpm lint` - 0 errors
+- [ ] `pnpm type-check` - 0 errors
+- [ ] `pnpm build` - production build succeeds
+- [ ] No `any` types in new code
+- [ ] No non-null assertions (`!`)
+- [ ] No `@ts-expect-error` or `@ts-ignore` comments
+- [ ] No `console.log` statements (use `logger`)
+- [ ] Tests pass (if applicable)
+
+---
+
+## Code Review Checklist
+
+- [ ] Types are explicit, not `any`
+- [ ] API inputs/outputs have Zod schemas
+- [ ] Error handling returns structured responses
+- [ ] No duplicate type definitions (import from source of truth)
+- [ ] Naming follows conventions (files: kebab-case, components: PascalCase)
+- [ ] Unused imports and dead code removed
+- [ ] No swallowed errors (silent `catch` blocks)
+
+---
+
+**Language**: All documentation must be written in **English**.