feat(cctv): add Iceland (Vegagerðin / IRCA) as a keyless CCTV source pack

One JSON list from gagnaveita.vegagerdin.is (about 500 camera views at roughly
170 road stations). Frames are JPEG stills in a single directory on
www.vegagerdin.is; only links inside that directory are registered, and the
media proxy pins the same directory.

The list decides ids, coordinates and which frame path is proxied, so it is
fetched over https with redirects refused and the body read capped at 2 MiB;
every rejection path releases the response body. Camera ids come from the frame
file name, which is unique per view in the live feed, and repeated frames
collapse before the cap.

The feed's view description (`Skyring`) is the label. An explicit Icelandic
facing ("til vesturs", "í suður", "séð austur") sets a high-confidence heading
(264 of 499 views); a view that states none, or two different ones, keeps the
id-hash low-confidence pose. A bare road direction ("Miklabraut austur") is not
read as a facing.

IRCA publishes road camera images under CC BY 4.0 and asks that the licensor is
acknowledged without implying endorsement; the attribution is in the Data
attribution popover and DATA_SOURCES.md, and every camera carries the licence
string. Default cap is 250 with anchors at Reykjavík and four regional centres so
a cap keeps every region. CCTV_ICELAND_ENABLED=0 turns the pack off.

Verified against the live feed through fetchCctvImageFromUpstream: 499 of 499
frames returned a JPEG, all distinct, all under 20 minutes old.

.env.example

@@ -238,6 +238,8 @@ AISSTREAM_API_KEY=
 # CCTV_CALGARY_ROWS_URL=                               # override the Open Calgary catalog URL
 # CCTV_CATALONIA_ENABLED=1                             # set 0 to disable the Servei Català de Trànsit cameras
 # CCTV_CATALONIA_MAX_SOURCES=150                       # cap cameras loaded from Catalonia (~130 exist today)
+# CCTV_ICELAND_ENABLED=1                               # set 0 to disable the Vegagerðin (Iceland) road cameras
+# CCTV_ICELAND_MAX_SOURCES=250                         # cap cameras loaded from Iceland (~500 views exist today)
 # CCTV_HK_ENABLED=1                                   # set 0 to disable the Hong Kong Transport Department cameras
 # CCTV_HK_MAX_SOURCES=1100                            # cap cameras loaded from Hong Kong (~1,013 exist today); min 8, max 1200
 # CCTV_HK_CAMERAS_URL=                                # override the DATA.GOV.HK camera locations XML URL