refactor(renderer): route all Phosphor icon imports through ui/icons barrel

Create src/renderer/components/ui/icons.ts as the single re-export point
for every Phosphor icon the renderer touches, then rewrite the 95 files
that previously imported directly from "@phosphor-icons/react" to pull
from the relative-path-to-barrel instead. The TitleBar commit earlier
in this series already used ui/icons; this commit extends the pattern
to the rest of the renderer.

Benefits now wired in:
  - one location where bundle tree-shaking can be reasoned about,
  - typos like Briefcase vs BriefCase show up against a finite list,
  - re-theming or swapping icon sets is a one-file edit,
  - a lint rule that flags raw @phosphor-icons/react imports can be
    added later without mass-rewriting call sites.

The barrel also re-exports the `Icon` type so call sites that type
icon props against the Phosphor component type work unchanged.

Test count stays at 363 passing; typecheck stays at 156 errors.

src/renderer/views/sections/ExecutionSections.tsx

@@ -5,7 +5,7 @@ import {
   Kanban,
   ListChecks,
   Target,
-} from "@phosphor-icons/react";
+} from "../../components/ui/icons";
 import { ConnectorEditor } from "../../components/connectors";
 import { KanbanBoard } from "../../components/dashboard";
 import { TwoPaneLayout } from "../../components/TwoPaneLayout";

src/renderer/views/sections/OrganizationSections.tsx

@@ -4,7 +4,7 @@ import {
   Target,
   UserPlus,
   Kanban,
-} from "@phosphor-icons/react";
+} from "../../components/ui/icons";
 import {
   AgentCreator,
   AgentEditor,