feat: add TypeBox/Ajv config schema package to the workspace (E00-S04-T01)

Adds packages/config (@personal-blog/config) — the EPPP configuration
service foundation. The package defines the configuration schema with
TypeBox (configSchema: host, port, databaseUrl, sessionSecret — the
validated config fields, golden-tuple pins @sinclair/typebox@0.34.52 and
ajv@8.20.0) and compiles it with Ajv (validateConfig). The environment
adapter (T04), field-specific startup errors (T02) and secret redaction
(T03) build on this boundary in later tasks; nothing reads process.env yet.

Wiring for the new workspace package: lockfile importer + resolved
typebox/ajv tree, apps/server/Dockerfile manifest copy (frozen in-image
install must match the lockfile importers), config-schema CI job, package
set fixtures (workspace-layout, workspace-config, strict-tsconfig,
typescript-pin), probe-file gitignore entry.

apps/server/Dockerfile

@@ -57,11 +57,12 @@ RUN corepack enable
 # invalidate the dependency layer, then install against the committed lockfile
 # (the same `--frozen-lockfile` path CI and developers use). Every workspace
 # package manifest is copied so the in-image workspace matches the lockfile
-# importers exactly (apps/server, packages/core, packages/database-postgres,
-# extensions/example).
+# importers exactly (apps/server, packages/core, packages/config,
+# packages/database-postgres, extensions/example).
 COPY package.json pnpm-lock.yaml pnpm-workspace.yaml tsconfig.base.json ./
 COPY apps/server/package.json apps/server/package.json
 COPY packages/core/package.json packages/core/package.json
+COPY packages/config/package.json packages/config/package.json
 COPY packages/database-postgres/package.json packages/database-postgres/package.json
 COPY extensions/example/package.json extensions/example/package.json
 RUN pnpm install --frozen-lockfile