Optimize root endpoint: add template caching and error handling

[Copilot]

Description

Addresses code review feedback from PR #19 by implementing performance and reliability improvements to the root endpoint:

• Template caching: Load HTML template once at startup instead of on every request
• Synchronous handler: Changed root() from async to sync (no async I/O performed)
• Error handling: Graceful degradation with 500 error if template fails to load

Before:

@app.get("/", response_class=HTMLResponse, include_in_schema=False)
async def root():
    html_path = Path(__file__).parent / "templates" / "index.html"
    return html_path.read_text()  # Disk I/O on every request, no error handling

After:

# Template loaded and cached at startup
_landing_page_template: str | None = None
try:
    html_path = Path(__file__).parent / "templates" / "index.html"
    _landing_page_template = html_path.read_text()
except Exception as e:
    logger.error("Failed to load landing page template from %s: %s", html_path, e)

@app.get("/", response_class=HTMLResponse, include_in_schema=False)
def root():
    if _landing_page_template is None:
        return HTMLResponse(
            content="Error: Unable to load the homepage template. Please contact the administrator.",
            status_code=500,
        )
    return _landing_page_template  # Serve from memory

Related Issue

Follow-up to PR #19 (review comments)

Motivation and Context

Original implementation had inefficient I/O patterns and lacked error handling. Template caching eliminates redundant disk reads; error handling prevents unhandled exceptions from missing/corrupted template files.

How Has This Been Tested?

• Application startup with successful template load
• Root endpoint returns cached HTML content
• Ruff linting passes

Screenshots (if appropriate):

Landing page functionality unchanged:

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• astral.sh
  • Triggering command: curl -LsSf REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)