fix(server): handle missing uhubctl + missing DYMO without traceback spam - #36

Local dev outside Docker doesn't have uhubctl on PATH. Without it,
every /api/power/status poll raised FileNotFoundError out of
find_or_recall_printer_port() — *before* the endpoint's try/except
caught it — and the frontend retried, producing a wall of tracebacks
on every page open.

Now:
- _run() logs a single WARNING the first time uhubctl isn't found,
  then re-raises FileNotFoundError unchanged
- find_printer_port() catches FileNotFoundError and returns None, so
  _printer_port_or_404 returns a clean 404 "Printer not detected"

The frontend already treats 404 as "hide the power-toggle UI" (see
PowerToggle.tsx:6-10), so this works without any client change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Address Copilot review on #36:

If state.json from a prior run on a uhubctl-equipped host has saved
_last_known_port, the previous version of find_or_recall_printer_port
would fall back to the cached port even when uhubctl had been removed.
The endpoint would then proceed to get_port_status()/power_*, which
also shell out via _run() → another FileNotFoundError → 500 with
traceback. Same symptom this PR aims to eliminate.

- find_printer_port now propagates FileNotFoundError (no longer hides
  it as None). Cleaner contract: the function does what it says.
- find_or_recall_printer_port catches FileNotFoundError → returns
  None, explicitly bypassing _last_known_port. /api/power/* then
  renders the same clean 404 as the no-cache path.
- Regression test test_find_or_recall_bypasses_cache_when_uhubctl_missing
  exercises the previously-broken scenario.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Address Copilot review: the previous message said "uhubctl not found on
PATH", which is misleading when UHUBCTL_BIN is set to an explicit path
that doesn't exist (no PATH lookup happens in that case). The new
wording is true for both scenarios and points at the env var as an
alternative remedy.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Copilot flagged the missing lock on the log-once latch. The race is
real but benign (microsecond window, self-limiting, max N duplicate
log lines per process lifetime) — same character of trade-off as the
existing unlocked _last_known_port. Document the choice in-place so
future readers don't have to re-derive it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…isible

Adding logger.info() in printer_service was effectively dead code in
production: Python's default root logger threshold is WARNING, so INFO
was silently dropped. Tests passed because pytest's caplog captures at
any level via propagation, regardless of root level — a misleading
green light.

Set logging.basicConfig in app.py before any module-level logger fires.
Default level INFO so service diagnostics show up; honor LOG_LEVEL env
var so production can dial it up or down.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…ple in dev

Earlier commit defaulted to INFO; the user point is that production
should be quieter and dev should be even chattier. Net result:

- app.py default LOG_LEVEL = WARNING (production-safe — operators only
  see things worth looking at, no noise from "no DYMO detected" INFO
  on every page load).
- .env.example sets LOG_LEVEL=DEBUG so `npm run dev` is verbose via the
  template that fresh contributors copy.

Also picks up Copilot's docstring nit: find_printer_port now says "the
uhubctl executable can't be found", matching the more general warning
wording instead of the over-narrow "isn't on PATH".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>