feat: French localization — community contribution by @OUARZA (#371)

The complete French dictionary contributed in #371 (1026 keys, zero empty
values, zero placeholder mismatches) lands as the second lazy locale on the
fr.ts + one static entry. The contributor's snapshot predated this week's
keys, so the 121 additions (device inbox #29, backdrop guard #39, junction
limits #331, lazy-editor toasts #353/#354, furniture #159) are translated
in this commit and flagged in the issue for the author's review; 21 stale
pre-#62 keys are dropped; key order follows en.json. The HA integration
translations file ships as contributed (full parity).

Wiring: loadFrench + __HOUSEPLAN_FR_RETRY_ASSET__ with the same 1/1
replacement guarantee as German; locale roles and localeRoots generalise to
(de|fr); the stale-entry fallback panel (#353) gains its French branch —
the r1 reviewer caught that this second hardcoded language list would have
silently degraded French to English on a cached entry. French profiles
(fr, fr-FR, fr-CA, fr-BE, fr-CH) select automatically.

Proofs: the registry-driven parity suite covers fr by construction
(1128/1128 keys); French analogues of both German-personal tests (product
glossary + non-translation scan with a reviewed equal-to-English
allow-list of 22 legitimate homographs); smoke_french_locale — fr-CA
profile commits French from the real bundle, one lazy chunk per page,
initial graph free of fr; smoke_entry_stale gains the French run; a
registry mutant drops the fr entry and is killed by the smoke. Initial
view: +0.5 KB (registry entry + fallback branch); the 23 KB dictionary is
lazy.

Issue: #371
User-Visible: yes

src/i18n/fr.ts

@@ -0,0 +1,6 @@
+import dictionary from './fr.json' with { type: 'json' };
+
+/** Must match the entry bundle before a lazy locale can be committed. */
+export const fingerprint = '__HOUSEPLAN_SOURCE_FINGERPRINT__';
+
+export { dictionary };

src/i18n/registry.ts

@@ -9,6 +9,7 @@ import {
 
 const BUILD_FINGERPRINT = '__HOUSEPLAN_SOURCE_FINGERPRINT__';
 const GERMAN_RETRY_ASSET = '__HOUSEPLAN_DE_RETRY_ASSET__';
+const FRENCH_RETRY_ASSET = '__HOUSEPLAN_FR_RETRY_ASSET__';
 
 export interface LanguageEntry {
   code: string;
@@ -24,6 +25,13 @@ async function loadGerman(attempt: 0 | 1): Promise<LazyLanguageModule> {
   return { dictionary: module.dictionary, fingerprint: module.fingerprint };
 }
 
+async function loadFrench(attempt: 0 | 1): Promise<LazyLanguageModule> {
+  const module = attempt === 0
+    ? await import('./fr')
+    : await import(/* @vite-ignore */ new URL(`${FRENCH_RETRY_ASSET}?retry`, import.meta.url).href);
+  return { dictionary: module.dictionary, fingerprint: module.fingerprint };
+}
+
 /**
  * The single runtime registry of shipped UI languages.
  *
@@ -34,6 +42,7 @@ export const LANGUAGE_REGISTRY = [
   { code: 'en', nativeLabel: 'English', dictionary: en },
   { code: 'ru', nativeLabel: 'Русский', dictionary: ru },
   { code: 'de', nativeLabel: 'Deutsch', loadDictionary: loadGerman },
+  { code: 'fr', nativeLabel: 'Français', loadDictionary: loadFrench },
 ] as const satisfies readonly LanguageEntry[];
 
 export type Lang = (typeof LANGUAGE_REGISTRY)[number]['code'];