feat(backend): support des providers OpenCode cloud (#92)

Ajoute le catalogue statique de providers OpenCode (lot B3), le stockage
sécurisé des secrets (SecretStore + adapter infrastructure), et les
use cases SaveOpenCodeProviderProfile/DeleteProfile câblés en composition
root. Couvre le fix B1 et les tests de régression demandés par QA.

cargo build --workspace propre, cargo test --workspace -- --test-threads=1
intégralement vert.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/backend/src/dto.rs

@@ -996,7 +996,8 @@ use application::{
     CloneOpenCodeProfileFromSeedInput, CloneOpenCodeProfileFromSeedOutput, ConfigureProfilesInput,
     ConfigureProfilesOutput, DeleteProfileInput, DetectProfilesInput, DetectProfilesOutput,
     FirstRunStateOutput, ListProfilesOutput, ProfileAvailability, ReferenceProfilesOutput,
-    SaveProfileInput, SaveProfileOutput,
+    SaveOpenCodeProviderProfileInput, SaveOpenCodeProviderProfileOutput, SaveProfileInput,
+    SaveProfileOutput,
 };
 use domain::profile::{AgentProfile, OpenCodeConfig};
 use domain::ProfileId;
@@ -1043,6 +1044,40 @@ impl From<CloneOpenCodeProfileFromSeedOutput> for ProfileDto {
     }
 }
 
+/// One entry of the static OpenCode cloud-provider catalogue (ticket #92, lot B3).
+#[derive(Debug, Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct OpenCodeProviderDto {
+    /// Identifier in the OpenCode provider registry (e.g. `"anthropic"`).
+    pub provider_id: String,
+    /// Human-readable label for the picker UI.
+    pub display_name: String,
+    /// Model names this provider serves, offered for selection.
+    pub models: Vec<String>,
+}
+
+impl From<application::OpenCodeProviderCatalogEntry> for OpenCodeProviderDto {
+    fn from(entry: application::OpenCodeProviderCatalogEntry) -> Self {
+        Self {
+            provider_id: entry.provider_id.to_owned(),
+            display_name: entry.display_name.to_owned(),
+            models: entry.models.iter().map(|&m| m.to_owned()).collect(),
+        }
+    }
+}
+
+/// A list of OpenCode cloud-provider catalogue entries (camelCase array on the
+/// wire).
+#[derive(Debug, Clone, Serialize)]
+#[serde(transparent)]
+pub struct OpenCodeProviderListDto(pub Vec<OpenCodeProviderDto>);
+
+impl From<application::ListOpenCodeProvidersOutput> for OpenCodeProviderListDto {
+    fn from(out: application::ListOpenCodeProvidersOutput) -> Self {
+        Self(out.providers.into_iter().map(Into::into).collect())
+    }
+}
+
 /// Request DTO for `detect_profiles`: the candidate profiles to probe.
 #[derive(Debug, Clone, Deserialize)]
 #[serde(rename_all = "camelCase")]
@@ -1105,6 +1140,39 @@ impl From<SaveProfileRequestDto> for SaveProfileInput {
     }
 }
 
+/// Request DTO for `save_opencode_provider_profile` (ticket #92, lot B3): the
+/// profile to upsert plus the literal provider fields. `apiKey` never reaches
+/// `profiles.json` — the use case seals it into the `SecretStore`.
+#[derive(Debug, Clone, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct SaveOpenCodeProviderProfileRequestDto {
+    /// The profile to create or replace (by id).
+    pub profile: AgentProfile,
+    /// Provider id in the OpenCode registry (e.g. `"anthropic"`).
+    pub provider_id: String,
+    /// Model name served by this provider.
+    pub model: String,
+    /// Literal API key, sealed into the `SecretStore` — never persisted as-is.
+    pub api_key: String,
+}
+
+impl From<SaveOpenCodeProviderProfileRequestDto> for SaveOpenCodeProviderProfileInput {
+    fn from(dto: SaveOpenCodeProviderProfileRequestDto) -> Self {
+        Self {
+            profile: dto.profile,
+            provider_id: dto.provider_id,
+            model: dto.model,
+            api_key: dto.api_key,
+        }
+    }
+}
+
+impl From<SaveOpenCodeProviderProfileOutput> for ProfileDto {
+    fn from(out: SaveOpenCodeProviderProfileOutput) -> Self {
+        Self(out.profile)
+    }
+}
+
 /// Request DTO for `clone_opencode_profile_from_seed`.
 #[derive(Debug, Clone, Deserialize)]
 #[serde(rename_all = "camelCase")]