Add AI-powered evidence description generation

Introduce a background worker that automatically generates
compliance-focused descriptions for uploaded evidence files
using configurable LLM providers. Descriptions are surfaced
across all interfaces: GraphQL API, MCP API, CLI, and the
console UI.

Key changes:
- Multi-provider LLM config with per-agent settings (pointer
  types for Temperature/MaxTokens to preserve zero values)
- Evidence description worker with bounded concurrency
- EvidenceDescriptionStatus typed enum with PostgreSQL enum type
- New `prb evidence` CLI commands (list, view, delete)
- Evidence description displayed in console table and preview
- Migration only marks evidences without files as completed

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/cmd/evidence/evidence.go

@@ -0,0 +1,36 @@
+// Copyright (c) 2025-2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package evidence
+
+import (
+	"github.com/spf13/cobra"
+	"go.probo.inc/probo/pkg/cmd/cmdutil"
+	"go.probo.inc/probo/pkg/cmd/evidence/delete"
+	"go.probo.inc/probo/pkg/cmd/evidence/list"
+	"go.probo.inc/probo/pkg/cmd/evidence/view"
+)
+
+func NewCmdEvidence(f *cmdutil.Factory) *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "evidence <command>",
+		Short: "Manage evidences",
+	}
+
+	cmd.AddCommand(list.NewCmdList(f))
+	cmd.AddCommand(view.NewCmdView(f))
+	cmd.AddCommand(delete.NewCmdDelete(f))
+
+	return cmd
+}