chore: initialize repository with project rules, docs, and phase-1 ADRs

Set up the foundation for the adastra-portal project:

- CLAUDE.md captures durable project rules (quality bar, security/perf/a11y
  as first-class, language, commit conventions, ADR proactivity).
- docs/ and decisions/ scaffolding with maintained indexes (docs/README.md
  and decisions/README.md), MADR 4.0.0 template, and tag vocabulary.
- Phase-1 ADRs (0001-0006) lock structural choices: ADR usage, Nx monorepo
  with the apps preset, naming convention (adastra-portal / portal-shell /
  portal-bff), Angular CSR/zoneless/Signals/Vitest, NestJS over Express,
  PostgreSQL with Prisma.
- docs/setup/ guides translated to English.
- .gitignore covers Node/Nx artifacts and the personal notes/ scratchpad.

The Nx workspace itself is not yet bootstrapped; that step is gated on a
revised setup guide aligned with the ADRs.

decisions/README.md

@@ -0,0 +1,52 @@
+# Architectural Decision Records
+
+This project records architecturally-significant decisions as **ADRs** in the [MADR 4.0.0](https://github.com/adr/madr) format. References: [adr.github.io](https://adr.github.io/).
+
+## Why ADRs
+
+ADRs capture the *why* behind a decision — context, drivers, options considered, trade-offs accepted — at the moment the decision is made. They make architecture reviewable, onboarding faster, and prevent the same debate from being re-litigated later.
+
+## Conventions
+
+- **Format:** MADR 4.0.0. Start from [template.md](template.md).
+- **Filename:** `NNNN-kebab-case-title.md`, e.g. `0007-adopt-tailwind-for-design-tokens.md`.
+- **Numbering:** globally sequential 4-digit prefix. Numbers never reset, never get reused — even when an ADR is superseded or deprecated.
+- **Layout:** flat folder. ADRs are not nested into category subfolders; topical organization happens via tags.
+- **Tags:** every ADR carries a `tags:` array in the MADR frontmatter, drawn from the [tag vocabulary](#tag-vocabulary) below. An ADR may carry several tags. Propose new tags (or renames) in the same PR that needs them; never invent ad-hoc tags inline.
+- **Status lifecycle:** `proposed` → `accepted` → optionally `deprecated` or `superseded by [ADR-NNNN](NNNN-other.md)`. Update the YAML frontmatter; never delete an ADR.
+- **Index maintenance:** every ADR addition or status change must update the [Index](#index) below in the same commit.
+
+## When to write an ADR
+
+Write one whenever a development decision is non-trivial: tool or library choice, framework pattern, security control, perf budget, a11y target, naming convention, deprecation, breaking change, or any choice that future contributors would benefit from understanding the *why* of.
+
+## Tag vocabulary
+
+The vocabulary below is the source of truth. It is intentionally coarse — propose extensions only when an existing tag genuinely doesn't fit, and avoid overly narrow tags.
+
+| Tag              | Scope |
+| ---------------- | ----- |
+| `frontend`       | UI, Angular, components, design system, client-side state |
+| `backend`        | API, BFF, server-side services |
+| `security`       | AuthN, AuthZ, sessions, CSP, dependency scanning, secret management |
+| `performance`    | Perf budgets, caching, bundle size, Lighthouse |
+| `accessibility`  | WCAG, a11y testing, keyboard, ARIA, contrast |
+| `infrastructure` | CI/CD, hosting, deployment, runtime |
+| `observability`  | Logs, metrics, traces, correlation IDs, monitoring |
+| `data`           | Persistence, schemas, migrations, data flow |
+| `process`        | Team conventions, workflows, repo policy |
+
+> _Status: starter vocabulary, to be refined as ADRs accumulate. Update this table whenever a tag is added, renamed, or retired._
+
+## Index
+
+ADRs are listed in numerical order. To slice by topic, filter on the `Tags` column.
+
+| #    | Title | Status | Tags | Date |
+| ---- | ----- | ------ | ---- | ---- |
+| [0001](0001-use-adrs-to-record-architectural-decisions.md) | Use ADRs to record architectural decisions | accepted | `process` | 2026-04-29 |
+| [0002](0002-adopt-nx-monorepo-apps-preset.md) | Adopt Nx monorepo with the `apps` preset | accepted | `infrastructure`, `frontend`, `backend` | 2026-04-29 |
+| [0003](0003-workspace-and-app-naming-convention.md) | Workspace and app naming convention | accepted | `process` | 2026-04-29 |
+| [0004](0004-frontend-stack-angular-csr-zoneless-signals.md) | Frontend stack — Angular (latest LTS), standalone, zoneless, Signals, CSR-only, Vitest | accepted | `frontend` | 2026-04-29 |
+| [0005](0005-backend-stack-nestjs.md) | Backend stack — NestJS over Express, Fastify, Hono | accepted | `backend` | 2026-04-29 |
+| [0006](0006-persistence-postgresql-prisma.md) | Persistence — PostgreSQL with Prisma | accepted | `data`, `backend` | 2026-04-29 |