feat(ai): phase 0 couche d'outils partagee (backend/tools) + tests

- backend/tools/: ToolContext, registry @tool + schemas JSON, audit ai_tool_call
- Services lecture/recherche: list_vaults, list_directory, read_file, search_fulltext, list_tags
- Permissions check_vault_access + resolve_safe_path, confirmation gating (two-step)
- Redaction des secrets, limites de taille, audit JSONL (args sensibles resumes)
- tests/test_tools.py: 30 tests (registry, contexte, execution, confirmation, audit)
- ROADMAP: item #79 phase A livree (A2 partiel)

backend/tools/schemas.py

@@ -0,0 +1,52 @@
+"""Pydantic input/output models for the AI tool layer.
+
+Input models double as JSON Schemas advertised to LLMs (via
+``model_json_schema``) and as validation for arguments received over MCP.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from pydantic import BaseModel, Field
+
+
+class ListVaultsInput(BaseModel):
+    """No parameters — lists the vaults the caller can access."""
+
+
+class ListDirectoryInput(BaseModel):
+    """Browse a directory inside a vault."""
+
+    vault: str = Field(..., description="Vault name")
+    path: str = Field("", description="Vault-relative directory path (empty = vault root)")
+
+
+class ReadFileInput(BaseModel):
+    """Read a text file's content from a vault."""
+
+    vault: str = Field(..., description="Vault name")
+    path: str = Field(..., description="Vault-relative file path")
+
+
+class SearchFulltextInput(BaseModel):
+    """Full-text search across one or all accessible vaults."""
+
+    q: str = Field(..., min_length=1, description="Search query")
+    vault: str = Field("all", description="Vault name or 'all'")
+    tag: str | None = Field(None, description="Optional comma-separated tag filter")
+    limit: int = Field(50, ge=1, le=200, description="Maximum number of results")
+
+
+class ListTagsInput(BaseModel):
+    """List tags and their occurrence counts."""
+
+    vault: str | None = Field(None, description="Vault name or 'all' (default: all accessible)")
+
+
+class ToolResult(BaseModel):
+    """Uniform result returned by :func:`backend.tools.registry.call_tool`."""
+
+    ok: bool = True
+    data: Any = None
+    error: str | None = None