Fix shell cd commands in npm scripts using subshells (#962)

The Docker browser build was failing because npm scripts used `cd app &&
command && cd ..`, which is unreliable in Docker RUN contexts and
certain shell environments.

## Changes

Updated all scripts using directory changes to use subshell isolation:

```diff
-"build:server": "npx tsc && cd app && npx webpack --config webpack.browser.config.mjs --mode production && cd ..",
+"build:server": "npx tsc && (cd app && npx webpack --config webpack.browser.config.mjs --mode production)",
```

**Updated scripts:**
- `build:server` - Docker browser build (primary fix)
- `build` - Electron build
- `install` - Dependency installation
- `test:app`, `test:backend` - Test runners (used in CI)
- `dev:app`, `dev:server:app` - Development servers

## Technical details

Subshell approach `(cd dir && command)`:
- Isolates directory change to subshell scope
- Auto-returns to parent directory on subshell exit
- More reliable across sh/bash/docker environments
- Eliminates manual `cd ..` restoration

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<details>

<summary>Original prompt</summary>

> The build is still failing, can't cd into app.


</details>



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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: thomasnordquist <7721625+thomasnordquist@users.noreply.github.com>

package.json

@@ -12,20 +12,20 @@
     "start:server": "npx tsc && node dist/src/server.js",
     "test": "yarn test:app && yarn test:backend",
     "test:all": "yarn test:app && yarn test:backend && yarn test:demo-video",
-    "test:app": "cd app && yarn test",
+    "test:app": "(cd app && yarn test)",
-    "test:backend": "cd backend && yarn test",
+    "test:backend": "(cd backend && yarn test)",
     "test:electron": "tsc && mocha --require source-map-support/register dist/src/spec/ui-tests.spec.js",
     "test:browser": "tsc && mocha --require source-map-support/register dist/src/spec/ui-tests.spec.js",
     "test:demo-video": "npx tsc && node dist/src/spec/demoVideo.js",
     "test:ui": "tsc && mocha --require source-map-support/register dist/src/spec/ui-tests.spec.js",
     "test:ui:vnc": "tsc && ./scripts/uiTestsWithVnc.sh",
     "test:mcp": "tsc && node dist/src/spec/testMcpIntrospection.js",
-    "install": "cd app && yarn && cd ..",
+    "install": "(cd app && yarn)",
     "dev": "npm-run-all --parallel dev:*",
-    "dev:app": "cd app && npm run dev",
+    "dev:app": "(cd app && npm run dev)",
     "dev:electron": "tsc && electron . --development",
     "dev:server": "npm-run-all --parallel dev:server:*",
-    "dev:server:app": "cd app && npx webpack-dev-server --config webpack.browser.config.mjs --mode development --progress",
+    "dev:server:app": "(cd app && npx webpack-dev-server --config webpack.browser.config.mjs --mode development --progress)",
     "dev:server:backend": "tsc && node dist/src/server.js",
     "lint": "npm-run-all --parallel lint:prettier lint:tslint lint:spellcheck",
     "lint:fix": "npm-run-all lint:tslint:fix lint:prettier:fix",
@@ -34,8 +34,8 @@
     "lint:tslint": "tslint -p ./",
     "lint:tslint:fix": "tslint -p ./ --fix",
     "lint:spellcheck": "cspell -e ./build -e \"node_modules\" \"**/*.ts{x,}\"",
-    "build": "tsc && cd app && yarn run build && cd ..",
+    "build": "tsc && (cd app && yarn run build)",
-    "build:server": "npx tsc && cd app && npx webpack --config webpack.browser.config.mjs --mode production && cd ..",
+    "build:server": "npx tsc && (cd app && npx webpack --config webpack.browser.config.mjs --mode production)",
     "prepare-release": "tsx scripts/prepare-release.ts",
     "package": "tsx package.ts",
     "ui-test": "./scripts/uiTests.sh",