fix(installer): quote browser env override paths

[tianma-if]

Fixes #57247.

Summary

• quote AGENT_BROWSER_EXECUTABLE_PATH when installers persist explicit browser overrides to .env
• keep the stale Snap override cleanup working for quoted and unquoted values
• add regression coverage for shell-sourcing spaced browser paths plus the PowerShell writer shape

Duplicate check

• checked open PRs for Installer writes unquoted AGENT_BROWSER_EXECUTABLE_PATH override into .env — spaced paths break shell source #57247 and AGENT_BROWSER_EXECUTABLE_PATH installer changes before opening
• only unrelated browser availability PR found (fix(tools): detect macOS app-bundle Chrome in browser availability gate #48185)

Tests

• .venv/bin/python -m pytest tests/test_install_sh_browser_install.py -q -k "browser_override or snap"
• .venv/bin/python -m pytest tests/test_install_sh_browser_install.py -q
• .venv/bin/python -m ruff check tests/test_install_sh_browser_install.py
• scripts/run_tests.sh tests/test_install_sh_browser_install.py -q

Note: pwsh is not installed in this local environment, so the PowerShell installer assertion is text-level coverage.

[alt-glitch]

This was generated by AI during triage.

Competing open fixes for #57247 (unquoted AGENT_BROWSER_EXECUTABLE_PATH breaks shell source on spaced paths) — for a maintainer to pick one:

• fix(install): quote AGENT_BROWSER_EXECUTABLE_PATH for spaced paths #57249 (earlier) — wraps the value in double quotes inline (="$path"), snap-strip regex generalized to "?/snap/.
• fix(installer): quote browser env override paths #57449 (this PR) — dedicated quote_dotenv_shell_value / ConvertTo-DotenvShellValue helpers using single quotes with '\'' escaping (handles embedded quotes), snap-strip regex generalized to (['\"])?/snap/ (both quote styles).

Same goal, different quoting mechanism — related_to, not a duplicate.

[teknium1]

Thanks for addressing the real spaced-path installer failure: current main still writes the POSIX override unquoted at scripts/install.sh:2109.

Problems

• The proposed single-quote splice is shell-safe but not safe for Hermes's runtime .env loader. Hermes calls python-dotenv at hermes_cli/env_loader.py:154-158 and :245-247; the linked discussion on fix(install): quote AGENT_BROWSER_EXECUTABLE_PATH for spaced paths #57249 documents that an apostrophe-containing path causes this form to drop the key under the pinned parser version. Please use escaped double quotes, consistent with hermes_cli/config.py:7610-7623.
• The added tests inspect installer source text, including the PowerShell check. AGENTS.md:1358-1392 explicitly bans source-reading tests. They do not validate either the PowerShell writer or the runtime dotenv path.

Suggested changes

• Cover a spaced path containing an apostrophe through both shell source and dotenv loading from a temporary HERMES_HOME.
• Replace source-shape assertions with executable behavior coverage.

Automated hermes-sweeper review.