feat(firebase)!: promote to v1.0.0 — cache auth.Client, adopt xerrors, bump deps to v1

Cache auth.Client in OnInit (eliminates per-probe app.Auth call in HealthCheck).
Replace all fmt.Errorf with xerrors structured errors (ErrInvalidInput / ErrInternal).
Bump health/launcher/logz to v1.0.1, add xerrors v1.0.1, Go directive to 1.26.
API committed as stable.

RELEASE.md

@@ -0,0 +1,55 @@
+# v1.0.0
+
+> `code.nochebuena.dev/go/firebase`
+
+## Overview
+
+`firebase` manages the lifecycle of a `firebase.google.com/go/v4` App: validates
+configuration at init time, initialises the SDK App, exposes the native `*firebase.App`
+to consumers, and performs health checks by probing the Firebase Auth service.
+
+v1.0.0 caches the `auth.Client` inside the component (eliminating per-probe allocation),
+adopts `xerrors` for all structured error returns, bumps all micro-lib dependencies to v1,
+and commits the API as stable.
+
+## What Changed Since v0.9.0
+
+### Auth client cached in `OnInit`
+
+`OnInit` now calls `app.Auth(context.Background())` once and stores the result on the
+component. `HealthCheck` uses the cached client directly — no per-probe `app.Auth(ctx)`
+call.
+
+### Structured errors via `xerrors`
+
+All `fmt.Errorf` calls replaced with `xerrors`:
+
+| Situation | Code |
+|-----------|------|
+| `ProjectID` empty | `ErrInvalidInput` |
+| `fb.NewApp` fails | `ErrInternal` (wraps SDK error) |
+| `app.Auth` fails | `ErrInternal` (wraps SDK error) |
+| `HealthCheck` before `OnInit` | `ErrInternal` |
+
+### Dependency updates
+
+- `health`, `launcher`, `logz` bumped from `v0.9.x` to `v1.0.1`
+- `xerrors v1.0.1` added as direct dependency
+- Go directive bumped from `1.25` to `1.26`
+
+## Full API (stable)
+
+- `Config` — `ProjectID string` (`FIREBASE_PROJECT_ID`, required)
+- `Provider` — `App() *fb.App`
+- `Component` — embeds `launcher.Component` + `health.Checkable` + `Provider`
+- `New(logger, cfg) Component`
+
+## Installation
+
+```
+go get code.nochebuena.dev/go/firebase@v1.0.0
+```
+
+## Changelog
+
+See [CHANGELOG.md](CHANGELOG.md#100---2026-05-12).