refactor: route raw Bun.file/write/hash/which/spawn through runtime shims

Eliminates 19 unguarded `Bun.*` runtime call sites in the plugin bundle
that crashed with `ReferenceError: Bun is not defined` under Electron.

Per-tool-call hot paths (executed on every Read/Edit):
- src/tools/hashline-edit/hash-computation.ts: Bun.hash.xxHash32 → bunHashXxh32
- src/tools/hashline-edit/hashline-edit-executor.ts: 8 sites via bunFile/bunWrite
- src/hooks/hashline-read-enhancer/hook.ts: Bun.file → bunFile
- src/hooks/hashline-edit-diff-enhancer/hook.ts: 2 sites via bunFile

Plugin-load paths:
- src/hooks/claude-code-hooks/config.ts and config-loader.ts: Bun.file → bunFile
- src/features/claude-code-mcp-loader/loader.ts: Bun.file → bunFile
- src/features/claude-code-plugin-loader/mcp-server-loader.ts: Bun.file → bunFile
- src/features/team-mode/deps.ts: Bun.spawn → spawn shim
- src/hooks/session-notification-utils.ts: Bun.which → bunWhich, also drops
  the bare `declare const Bun` ambient declaration
- src/shared/binary-downloader.ts: Bun.write → bunWrite

Pure mechanical API swaps. No control-flow or signature changes.

src/tools/hashline-edit/hash-computation.ts

@@ -1,12 +1,13 @@
 import { HASHLINE_DICT } from "./constants"
 import { createHashlineChunkFormatter } from "./hashline-chunk-formatter"
+import { bunHashXxh32 } from "../../shared/bun-hash-shim"
 
 const RE_SIGNIFICANT = /[\p{L}\p{N}]/u
 
 function computeNormalizedLineHash(lineNumber: number, normalizedContent: string): string {
   const stripped = normalizedContent
   const seed = RE_SIGNIFICANT.test(stripped) ? 0 : lineNumber
-  const hash = Bun.hash.xxHash32(stripped, seed)
+  const hash = bunHashXxh32(stripped, seed)
   const index = hash % 256
   return HASHLINE_DICT[index]
 }

src/tools/hashline-edit/hashline-edit-executor.ts

@@ -1,5 +1,6 @@
 import type { ToolContext } from "@opencode-ai/plugin/tool"
 import { publishToolMetadata } from "../../features/tool-metadata-store"
+import { bunFile, bunWrite } from "../../shared/bun-file-shim"
 import { applyHashlineEditsWithReport } from "./edit-operations"
 import { countLineDiffs, generateUnifiedDiff } from "./diff-utils"
 import { canonicalizeFileText, restoreFileText } from "./file-text-canonicalization"
@@ -94,7 +95,7 @@ export async function executeHashlineEditTool(args: HashlineEditArgs, context: T
 
     const edits = deleteMode ? [] : normalizeHashlineEdits(args.edits)
 
-    const file = Bun.file(filePath)
+    const file = bunFile(filePath)
     const exists = await file.exists()
     if (!exists && !deleteMode && !canCreateFromMissingFile(edits)) {
       return `Error: File not found: ${filePath}`
@@ -102,7 +103,7 @@ export async function executeHashlineEditTool(args: HashlineEditArgs, context: T
 
     if (deleteMode) {
       if (!exists) return `Error: File not found: ${filePath}`
-      await Bun.file(filePath).delete()
+      await bunFile(filePath).delete()
       return `Successfully deleted ${filePath}`
     }
 
@@ -122,11 +123,11 @@ export async function executeHashlineEditTool(args: HashlineEditArgs, context: T
 
     const writeContent = restoreFileText(canonicalNewContent, oldEnvelope)
 
-    await Bun.write(filePath, writeContent)
+    await bunWrite(filePath, writeContent)
 
     if (pluginCtx?.client) {
       await runFormattersForFile(pluginCtx.client as FormatterClient, context.directory, filePath)
-      const formattedContent = Buffer.from(await Bun.file(filePath).arrayBuffer()).toString("utf8")
+      const formattedContent = Buffer.from(await bunFile(filePath).arrayBuffer()).toString("utf8")
       if (formattedContent !== writeContent) {
         const formattedEnvelope = canonicalizeFileText(formattedContent)
         const formattedMeta = buildSuccessMeta(
@@ -138,8 +139,8 @@ export async function executeHashlineEditTool(args: HashlineEditArgs, context: T
         )
         await publishToolMetadata(metadataContext, formattedMeta)
         if (rename && rename !== filePath) {
-          await Bun.write(rename, formattedContent)
-          await Bun.file(filePath).delete()
+          await bunWrite(rename, formattedContent)
+          await bunFile(filePath).delete()
           return `Moved ${filePath} to ${rename}`
         }
         return `Updated ${filePath}`
@@ -147,8 +148,8 @@ export async function executeHashlineEditTool(args: HashlineEditArgs, context: T
     }
 
     if (rename && rename !== filePath) {
-      await Bun.write(rename, writeContent)
-      await Bun.file(filePath).delete()
+      await bunWrite(rename, writeContent)
+      await bunFile(filePath).delete()
     }
 
     const effectivePath = rename && rename !== filePath ? rename : filePath