perf: reduce streaming render cost and refresh activity page on demand

- Segment streaming Markdown so completed blocks are reused and only the growing tail is re-parsed; fall back to whole-document parsing for document-wide constructs
- Memoize conversation sidebar rows and cache per-conversation derived activity, ordering and pending approvals
- Activity page loads on entry, refreshes every 15 s while visible, and has a single header refresh button
- Include pending settings, model download source, device sharing and knowledge gateway changes in the working tree
- Add Electron streaming input benchmark and regression tests

tests/streaming-input.electron.test.ts

@@ -0,0 +1,49 @@
+// @vitest-environment node
+import { spawn } from 'node:child_process'
+import { mkdtemp, rm } from 'node:fs/promises'
+import { createRequire } from 'node:module'
+import { tmpdir } from 'node:os'
+import { join, resolve } from 'node:path'
+import react from '@vitejs/plugin-react'
+import { build as bundle } from 'esbuild'
+import { build } from 'vite'
+import { expect, it } from 'vitest'
+
+it('benchmarks native input during main-driven streaming at 16/32/50/80ms', async () => {
+  const directory = await mkdtemp(join(tmpdir(), 'goodbuddy-streaming-input-'))
+  try {
+    await build({
+      configFile: false, root: resolve('tests/support'), base: './',
+      plugins: [react()], logLevel: 'error',
+      build: { outDir: join(directory, 'renderer'), emptyOutDir: true,
+        rollupOptions: { input: resolve('tests/support/streaming-input-page.html') } }
+    })
+    await bundle({ entryPoints: [resolve('tests/support/streaming-input-driver.ts')],
+      outfile: join(directory, 'driver.mjs'), bundle: true, platform: 'node', format: 'esm',
+      external: ['electron'] })
+    await bundle({ entryPoints: [resolve('tests/support/streaming-input-preload.ts')],
+      outfile: join(directory, 'preload.cjs'), bundle: true, platform: 'node', format: 'cjs',
+      external: ['electron'] })
+    const env: NodeJS.ProcessEnv = { ...process.env, GOODBUDDY_STREAMING_INPUT_DIRECTORY: directory }
+    delete env.ELECTRON_RUN_AS_NODE
+    const child = spawn(createRequire(import.meta.url)('electron'), [join(directory, 'driver.mjs')],
+      { env, stdio: ['ignore', 'pipe', 'pipe'] })
+    let output = ''
+    child.stdout.on('data', data => { output += data })
+    child.stderr.on('data', data => { output += data })
+    const timeout = setTimeout(() => child.kill(), 100_000)
+    try {
+      const code = await new Promise((resolve, reject) => {
+        child.once('exit', resolve)
+        child.once('error', reject)
+      })
+      process.stdout.write(output.split(/\r?\n/u).filter(line => line.startsWith('Streaming input ')).join('\n') + '\n')
+      expect(code, output).toBe(0)
+    } finally {
+      clearTimeout(timeout)
+      if (child.exitCode === null) child.kill()
+    }
+  } finally {
+    await rm(directory, { recursive: true, force: true })
+  }
+}, 120_000)