URL-parameter loads (`/skewt?q=…`) were blocking the initial mount
on three serial steps: geocoder/grid resolve, ProfilesFile or
HrrrProfileLookup read, and the SkewtParams/SoundingParams/SkewtSvg
derivation. The address path in particular hits an external API,
which made the page take "forever" to load on first paint.
Restructure SkewtLive so the page chrome (header, search bar) renders
synchronously on mount, and the heavy work runs in a single
`start_async(:load_skewt, …)` task that calls SkewtLocationResolver,
walks the on-disk profile store with a DB fallback, and produces the
SVG. A new `loading?` assign drives a small spinner + "Resolving
location and loading HRRR profile…" message that shows while the task
is in flight; previous data stays on screen so navigation between
forecast hours doesn't blank out the diagram.
handle_async/3 covers three landings:
* `{:ok, {:ok, result}}` — apply assigns from the resolver
* `{:ok, {:error, reason}}` — surface as the existing error alert
(geocoder failure, unknown callsign, etc.)
* `{:exit, reason}` — log a warning and show a generic retry message
start_async/3 cancels any prior task with the same name on each call,
so a rapid-fire URL patch (e.g. clicking through forecast-hour
buttons before the first response returns) never lands stale data.
Tests: extended SkewtLiveTest from 3 to 4 cases — the URL-param
initial render now asserts the chrome + spinner appear pre-async,
and a separate case `render_async/2`s the view to confirm the
location label arrives once the task completes. 4/4 green.
Single search bar accepts an address, Maidenhead grid square, or
callsign; resolves it to lat/lon via Geocoder / Maidenhead /
CallsignLocation (cheapest classification first), snaps to the HRRR
grid via the existing ProfilesFile reader, and renders an SVG
Skew-T-Log-P with isobars, skewed isotherms, dry/moist adiabats, and
mixing-ratio lines. A button row picks between every available
forecast hour (now → f18); default is the most recent analysis.
Right pane lists derived stability and refractivity stats from
SoundingParams.derive (PWAT, BL depth, K-index, lifted index, min
dN/dh, ducting status + per-duct base/top/ΔM).
Renderer is server-side SVG so the page works without JS and serializes
into the LiveView payload as a single tag. Wind barbs are deliberately
omitted — HRRR's persisted profile carries wind only at 10 m AGL.
