PictView WIC support and backfill list

Current behaviour

PictView no longer uses the historical PVW32DLL decoder set. On every plug-in connection it enumerates the local WIC decoder inventory through IWICBitmapDecoderInfo::GetFileExtensions and uses those masks for both the viewer and thumbnail loader.

Consequences:

A codec installed by the user or Windows (for example WebP, HEIF/HEIC, DNG or a camera RAW codec) is picked up automatically at the next Salamander start. It is not necessary to add its extension to a static list.
If that codec is uninstalled, the corresponding PictView association is removed on the next start.
The built-in WIC baseline is BMP (.bmp, .dib, .rle), GIF, ICO, JPEG (.jpg, .jpe, .jpeg, .jfif), PNG, TIFF (.tif, .tiff), JPEG XR / HD Photo (.jxr, .wdp) and WIC-compatible DDS. The runtime inventory remains the source of truth for the exact extensions on an individual computer.

Legacy formats requiring an implementation or a WIC codec

The old static registration advertised 114 masks. The masks below are not part of the guaranteed native WIC baseline, so the current backend must not claim them unless a locally installed WIC decoder advertises the mask. To restore platform-independent PictView support, implement a decoder/rasterizer in PictView (or bundle and maintain an appropriate codec), add test files, and then add the capability to the comparison page.

2BP, 82I, 83I, 85I, 86I, 89I, 92I,
AI, ANI, ARW, AWD,
BLP, BMI, BW,
CAL, CALS, CDR, CDT, CEL, CIT, CLK, CLP, CMX, COT, CPT, CR2, CRW, CUR, CUT,
DCX, DNG, DTX,
EPS, EPT,
FLC, FLI,
GEM,
HAM, HMR, HPI, HRZ,
ICN, IFF, IMG, ITIFF,
JFF, JIF, JMX,
LBM,
MAC, MACP, MBM, MIL, MNG, MOV, MPNT, MSP,
NEF,
OFX, ORF,
PAINT, PAN, PAT, PBM, PC2, PCD, PCT, PCX, PEF, PGM, PIC, PICT, PNM, PNTG,
PPM, PSP*, PSD, PYX,
QFX,
RAF, RAS, RGB,
SAM, SCX, SEP, SGI, SKA, ST, STW, SUN,
TGA, THM, THUMB,
UDI,
WBMP, WEB, WPG,
XAR,
ZBR, ZMF, ZNO.

Formats that need special treatment

Format family	Status and required work
WebP	Supported automatically only when the Windows WebP WIC codec is installed. Do not advertise it as universal support. A bundled decoder would make it guaranteed. Official Microsoft codec available in Microsoft Store.
HEIF/HEIC, AVIF	Not historically registered. They become available automatically if their WIC extension codec exposes a mask. Add test files before describing them as a product guarantee.
DNG and camera RAW	May be exposed by a WIC Raw Image Extension or vendor codec. Native decoding is required for a consistent guarantee across machines. Official Microsoft codec available in Microsoft Store.
SVG	Not a WIC bitmap decoder. Restore thumbnails/viewing only through an SVG rasterizer or a dedicated thumbnail implementation. Functionally replaceable with WebView2 Render Viewer. PictView could implement Viewer Frame component from Salamatrix framework which provides shared WebView2 capability.
DDS	The WIC decoder supports only WIC-compatible DDS variants. Test each required DXGI compression format before promising full DDS support.
EPS/EPT/AI, MOV	The previous implementation relied on embedded previews. Proper rendering needs a PostScript/PDF/vector rasterizer and a video-frame decoder, respectively.

Maintenance rule

Do not add a new PictView suffix by hand merely because an old table listed it. Either let WIC enumerate it from an installed decoder, or add a tested native implementation and document its exact feature limits.