Narrow scope to radar, and put the app on a real OpenStreetMap base map

Drops forecasts, lightning, the home-screen widget and advertising. What
remains is radar on a map, the official ARPA alert bulletin, and rain
notifications.

The base map is now OpenFreeMap's Positron style: real OpenStreetMap vector
tiles with no API key, no registration, no request limits and commercial use
permitted. Every other free tier — MapTiler, Stadia, Jawg, Thunderforest —
needs a key, which is a secret to manage, a quota to outgrow and a signup to
complete before anyone can build the project, and the map is the one thing the
app cannot work without. Positron rather than Liberty or Bright because the
radar overlay has to be the loudest thing on screen, and a desaturated grey
base is built to sit under data.

Its style JSON carries no `attribution` field, so MapLibre displays no credits
by itself. The app renders them from the region config instead: the two
mandatory credits, OpenStreetMap and OpenMapTiles, go in the always-visible
bar, and OpenFreeMap's own credit — optional by their terms — is listed on the
Sources screen with the rest. The bundled offline style is still reachable with
MAP_STYLE_URL=offline, and still claims no base map attribution, because
crediting OpenStreetMap while showing it would be a false claim.

Radar-DPC stays the source. ARPA Piemonte's own radar remains a disabled stub
for two reasons that belong to the project owner, not to the code: the
real-time access link is only issued by email, and the open-data page states
the data is "gratuiti" and nothing else. Free of charge is not a licence, and
rendering those volumes into frames served from a CDN is redistribution. Both
questions go in the same email. An earlier draft of the docs recorded ARPA
radar as CC BY 4.0; the source page does not support that, so the claim is
removed rather than carried forward.

The documentation is updated throughout rather than annotated: CLAUDE.md gains
an explicit scope boundary, data-sources drops MET Norway and ISTAT and gains
the base map, licenses records that free of charge is not a licence, privacy
loses the whole advertising section, and the roadmap is renumbered so the
backend worker is next — until it exists, DpcRadarSource has nothing to read.

licenses.md keeps Open-Meteo and Blitzortung listed as excluded even though the
features that would have used them are gone: both are non-commercial-only, ads
are a plausible future, and neither should be adopted on the grounds that there
are none today.

Verified: analyze clean, 130 tests passing, and on the emulator the radar
overlay sits correctly over Piedmont on real OSM tiles with Turin, Milan and
Genoa labelled, the age reads "Aggiornato 4 minuti fa", and the Sources screen
lists all five credits with their licences.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Nuvolari/docs/licenses.md

@@ -9,11 +9,11 @@ to save screen space.
 | Data | License | Mandatory credit | Notes |
 |---|---|---|---|
 | Radar-DPC rasters | CC BY-SA | "Radar-DPC" | **Share-alike propagates to our frames** |
-| ARPA Piemonte radar | CC BY 4.0 | "Fonte: Arpa Piemonte - www.arpa.piemonte.it" | Adapter disabled, unused |
-| MET Norway forecast | CC BY 4.0 | "MET Norway" | Identifying User-Agent required |
-| ItaliaMeteo ICON-2I | CC BY 4.0 | "ItaliaMeteo-ARPAE" | Fallback, behind a flag |
+| ARPA Piemonte radar | **none stated** | — | Adapter disabled; see below |
 | ARPA Piemonte alerts | not stated | "Arpa Piemonte" + link to the official bulletin | Levels republished verbatim |
-| OpenStreetMap base map | ODbL | "© OpenStreetMap contributors" | Must stay visible on the map |
+| OpenStreetMap data | ODbL | "© OpenStreetMap contributors" | Must stay visible on the map |
+| OpenMapTiles schema | BSD 3-Clause | "© OpenMapTiles" | Must stay visible on the map |
+| OpenFreeMap service | MIT | "OpenFreeMap" — optional | Listed on the Sources screen |
 
 ## Share-alike is the constraint that shapes the backend
 
@@ -25,23 +25,45 @@ consequences:
 - We cannot relicense them, and we cannot restrict their reuse.
 - The share-alike obligation covers the **data**, not the app's source code or UI.
 
-## MET Norway User-Agent
+The manifest carries its own `attribution` string for exactly this reason: the credit
+travels with the frames rather than being remembered at render time, and the app
+displays whatever the publisher of those frames says to display.
 
-MET Norway blocks generic User-Agent strings. Requests must carry an identifying
-string with a real contact address:
+## ARPA Piemonte radar: free of charge is not a licence
 
-```
-Nuvolari/<version> (<contact address>)
-```
+The ARPA open-data page describes the radar volumes as *gratuiti* and says nothing about
+reuse terms. That is not permission to redistribute. Rendering those volumes into frames
+and serving them from our CDN to app users **is** redistribution.
 
-The contact comes from `METNO_USER_AGENT_CONTACT` in `env.json` and is never hardcoded.
-The `Expires` header must be honoured — re-requesting before expiry risks a block.
+So the adapter stays disabled until ARPA states terms, and the email that requests the
+access link should ask for the reuse terms in the same breath. Both are the project
+owner's to obtain — see [data-sources.md](data-sources.md) section 2.
 
-## Not usable
+An earlier draft of this file recorded ARPA radar as CC BY 4.0. The source page does not
+support that, so the claim has been removed rather than carried forward.
 
-- **Blitzortung** — commercial use prohibited. This app carries ads, so it is
-  commercial. Never integrate it.
-- **Open-Meteo free tier** — non-commercial only. Same reasoning.
+## Base map credits are not automatic
+
+The OpenFreeMap style JSON has no `attribution` field, so MapLibre displays nothing on
+its own. The app renders the credits itself:
+
+- the always-visible attribution bar carries the two **mandatory** credits;
+- the Sources screen lists all three with their licences and links.
+
+The bar lists only what is actually on screen. With the offline fallback style there is
+no OpenStreetMap data being displayed, so crediting OpenStreetMap there would be a false
+attribution — the bar says "Mappa base non configurata" instead.
+
+## Advertising, and why it still matters here
+
+The app currently carries **no advertising**, so it is not a commercial product today.
+Ads are a plausible future, though, and a source adopted now on non-commercial terms
+would have to be ripped out then. Prefer sources that permit commercial use.
+
+This is why **Open-Meteo's free tier** and **Blitzortung** remain listed as excluded even
+though the features that would have used them are out of scope: both are
+non-commercial-only, and neither should be reached for on the grounds that there are no
+ads at the moment.
 
 ## Naming and independence