feat(skill-awareness): T1→T5 — manifeste de skills + outil MCP idea_skill_read

Surface les skills assignés à un agent « à la MCP » : description sur l'entité
Skill (+ effective_description fallback), section « # Skills disponibles » haute
altitude dans le convention-file (mode MCP), outil read-only idea_skill_read
(résolution projet→global), use case ReadSkill (port SkillStore existant), et
câblage au composition root. Dump legacy du corps complet conservé en mode
sans-MCP (zéro régression). Rétro-compat index.json (serde default).

Tests : domain+application+infrastructure 1212 passed / 0 failed (23 ajoutés).
Reste : T6 (champ description front) + T7 (e2e après rebuild AppImage).

NB topologie : commit réalisé par l'orchestrateur car l'agent Git était
injoignable (bug de livraison cold-start) ; à faire relire/rebaser par Git.

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

crates/infrastructure/src/orchestrator/mcp/tools.rs

@@ -51,7 +51,11 @@ pub enum ToolMapError {
 pub fn tool_returns_reply(tool: &str) -> bool {
     matches!(
         tool,
-        "idea_ask_agent" | "idea_list_agents" | "idea_context_read" | "idea_memory_read"
+        "idea_ask_agent"
+            | "idea_list_agents"
+            | "idea_context_read"
+            | "idea_memory_read"
+            | "idea_skill_read"
     )
 }
 
@@ -201,6 +205,21 @@ pub fn catalogue() -> Vec<ToolDef> {
                 "additionalProperties": false
             }),
         },
+        ToolDef {
+            name: "idea_skill_read",
+            description: "Read the full body of an IdeA skill assigned to you, by name — call this \
+                          to actually execute/follow a skill listed in your « Skills disponibles » \
+                          section. Resolves project scope first, then global. Returns the skill's \
+                          Markdown inline.",
+            input_schema: json!({
+                "type": "object",
+                "properties": {
+                    "name": { "type": "string", "description": "Skill name (as listed in your context)." }
+                },
+                "required": ["name"],
+                "additionalProperties": false
+            }),
+        },
         ToolDef {
             name: "idea_create_skill",
             description: "Create a reusable IdeA skill (Markdown) in the project or global scope.",
@@ -320,6 +339,14 @@ pub fn map_tool_call(
             content: s("content"),
             ..base()
         },
+        "idea_skill_read" => OrchestratorRequest {
+            request_type: Some("skill.read".to_owned()),
+            // The requester (handshake identity) is carried for symmetry with the
+            // other read tools; `validate` derives the requester party from it.
+            requested_by: Some(requester.to_owned()),
+            name: s("name"),
+            ..base()
+        },
         "idea_create_skill" => OrchestratorRequest {
             request_type: Some("skill.create".to_owned()),
             name: s("name"),