feat: GET /api/v2/agent-firewall/sessions/{id} (#24814)

Add a GET endpoint at `/api/v2/agent-firewall/sessions/{id}` that
returns agent firewall session metadata (`id`, `workspace_id`,
`owner_id`, `confined_process`, `started_at`). The handler authorizes
against the `boundary_log` resource with `ActionRead` via dbauthz.

The endpoint is enterprise-only, gated behind the `FeatureBoundary`
entitlement.

The `GetBoundarySessionByID` SQL query JOINs through `workspace_agents`
→ `workspace_resources` → `workspace_builds` → `workspaces` to return
`workspace_id` and `workspace_owner_id` directly, avoiding a separate
query.

Also adds an `owner_id` column to the `boundary_logs` table (migration
000526) with a FK to `users(id)` and a backfill from
`boundary_sessions`. This enables user-scoped RBAC authorization for
`InsertBoundaryLogs` via `.WithOwner()`, ensuring workspace agents can
only insert logs for their own owner.

Depends on #24810

**RBAC behaviour:**

| Role    | Result |
|---------|--------|
| Owner   | read   |
| Auditor | read   |
| Member  | 404    |

> [!NOTE]
> This PR was authored by Coder Agents.

coderd/database/querier.go

@@ -367,7 +367,7 @@ type sqlcQuerier interface {
 	// limits roots, not total family members.
 	GetAutoArchiveInactiveChatCandidates(ctx context.Context, arg GetAutoArchiveInactiveChatCandidatesParams) ([]GetAutoArchiveInactiveChatCandidatesRow, error)
 	GetBoundaryLogByID(ctx context.Context, id uuid.UUID) (BoundaryLog, error)
-	GetBoundarySessionByID(ctx context.Context, id uuid.UUID) (BoundarySession, error)
+	GetBoundarySessionByID(ctx context.Context, id uuid.UUID) (GetBoundarySessionByIDRow, error)
 	GetChatACLByID(ctx context.Context, id uuid.UUID) (GetChatACLByIDRow, error)
 	// GetChatAdvisorConfig returns the deployment-wide runtime configuration
 	// for the experimental chat advisor as a JSON blob. Callers unmarshal the