feat: finalise ticket99 - implémentation agent model configuration v2

- agent/lifecycle.rs: lifecycle management per profile
- agent/provider_catalogue.rs: provider registration with model support
- agent/usecases.rs: usecases for profile-based agent invocation
- agent/mod.rs: expose agent capabilities via AgentManager
- backend/dto.rs: AgentModelConfig, AgentProviderConfig DTOs
- domain/profile.rs: extend Profile avec agent capabilities
- domain/permission.rs: permission checks pour agent access
- infrastructure/assistant/mod.rs: agent integration
- infrastructure/permission/{claude,codex}.rs: permission handlers
- web-server/lib.rs: agent endpoints
- commands.rs: agent commands
- frontend/adapters/{http,profile,mock,domain}.ts: adapters
- frontend/first-run/FirstRunWizard.{test.tsx,tsx}: first-run flow

crates/domain/src/permission.rs

@@ -853,12 +853,6 @@ pub struct ProjectionContext<'a> {
     /// Optional model selected by the agent profile. Orthogonal to permissions:
     /// projectors may still materialise it even when `eff == None`.
     pub model: Option<&'a str>,
-    /// Optional Codex `model_provider` value selected by the profile.
-    pub model_provider: Option<&'a str>,
-    /// Optional base URL for a custom Codex model provider.
-    pub model_provider_base_url: Option<&'a str>,
-    /// Optional API-key environment variable name for a model provider.
-    pub model_provider_env_key: Option<&'a str>,
 }
 
 /// One file a projector wants materialised at launch, tagged by **ownership**.