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/components/communication/composer-shell/ComposerShell.tsx

@@ -1,5 +1,5 @@
 import { forwardRef, useCallback, type ReactNode, type KeyboardEvent, type ChangeEvent } from "react";
-import { PaperPlaneTilt } from "@phosphor-icons/react";
+import { PaperPlaneTilt } from "../../ui/icons";
 import { ActionButton, InlineNotice } from "../../ui";
 
 export interface ComposerShellProps {