v0.257.0: the app catalog can speak English (R-560, slice 5 Part A)

The READ PATH for a second language in `.felhom.yml`. An `i18n: {en: …}` sibling
block inside the same file; `Metadata.For(lang)` merges it FIELD BY FIELD over the
Hungarian, so a missing or blank English field shows the Hungarian one and a
half-translated app is a legal, shippable state.

`For("hu")` is the parsed struct with `I18n` cleared and nothing else — measured
against all 53 real catalog files, copied into `internal/stacks/testdata/catalog/`.
Lists replace whole; every other list is matched by its own key, never by position.
`For` never writes through the receiver: the metadata is the stack manager's, shared
by concurrent requests, and an in-place merge would leak one household's language
into another household's page.

Pages reach catalog copy only through `LocalizeStacks`/`LocalizeStackPtr`/`MetaFor`,
and `TestNoDirectMetaCopyReadOnPages` keeps a named, reasoned allow-list of every
direct `.Meta.<copy>` read in `internal/web` so the NEXT page to read one fails the
suite instead of quietly rendering Hungarian to an English household.

Eight red-proofs. Two of them convicted a hollow TEST rather than the code: a struct
copy shares its slices' backing arrays, so the obvious DeepEqual mutation check
passed a deliberately broken merge; and a one-entry fixture cannot tell key matching
from position matching. Both rewritten, both then seen to fail.

MinAgent: 0.131.0 (unchanged). Older controllers are unaffected — `LoadMetadata`
uses non-strict `yaml.Unmarshal`, so a pre-0.257.0 box drops the whole block.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/stacks/testdata/catalog/code-server/.felhom.yml

@@ -0,0 +1,75 @@
+# =============================================================================
+# .felhom.yml - App metadata for felhom-controller
+# =============================================================================
+
+# --- Display info (shown on dashboard) ---
+display_name: "Code-Server"
+description: "VS Code a böngészőben - kódolás bárhonnan"
+category: "dev"
+subdomain: "code"
+slug: "code-server"
+# catalog_since: the date THIS repo last changed this app's pinned images. Any commit that
+# changes an image: line must set this to the same day (see CLAUDE.md).
+catalog_since: "2026-07-18"
+
+# --- Resource hints (displayed on deploy screen) ---
+resources:
+  mem_request: "200M"
+  mem_limit: "1024M"
+  pi_compatible: false
+  needs_hdd: false
+
+# --- Deploy fields (first deployment only) ---
+deploy_fields:
+  - env_var: DOMAIN
+    label: "Domain"
+    type: domain
+    description: "A szerver domain neve"
+    locked_after_deploy: true
+
+  - env_var: SUBDOMAIN
+    label: "Aldomain"
+    type: subdomain
+    default: "code"
+    required: true
+    locked_after_deploy: true
+    description: "Az alkalmazás aldomainje"
+
+  - env_var: PASSWORD
+    label: "Hozzáférési jelszó"
+    type: password
+    generate: "password:16"
+    description: "Bejelentkezési jelszó a szerkesztőhöz."
+    locked_after_deploy: false
+
+# --- App info (info page content) ---
+app_info:
+  tagline: "VS Code a böngészőben - teljes fejlesztői környezet bárhonnan"
+  default_creds: "(telepítéskor generált jelszó)"
+  docs_url: "https://coder.com/docs/code-server/"
+
+  use_cases:
+    - 'Kódolás bárhonnan, bármilyen eszközről böngészőben'
+    - 'VS Code teljes funkcionalitás - bővítmények, terminál, debug'
+    - 'Távoli fejlesztés alacsony sávszélességű kapcsolaton is'
+    - 'Egységes fejlesztői környezet több eszközről'
+    - 'Tableten és iPaden is használható'
+
+  first_steps:
+    - 'Nyisd meg a code.DOMAIN címet a böngészőben'
+    - 'Add meg a hozzáférési jelszót'
+    - 'Nyisd meg a terminált (Ctrl+`) és telepíts eszközöket'
+    - 'Telepíts bővítményeket az Extensions panelben'
+
+  prerequisites:
+    - 'x86 processzor szükséges a legjobb teljesítményhez'
+    - 'Legalább 1 GB szabad RAM ajánlott'
+
+# --- Controller-side health probe ---
+healthcheck:
+  checks:
+    - type: api
+      port: 8443
+      path: "/healthz"
+      expect:
+        status: 200