#745: import Targa (.tga) and Radiance HDR (.hdr) stills and sequences

[vangel76]

Fixes #745.

Part of ranked gap #17 "Media Browser lists files import refuses" (docs/gaps.md).

Problem

The Media Browser lists .tga and .hdr files (and image-sequence detection groups them), but media::is_importable had neither extension and the still decoder never tried them, so importing a Targa or Radiance HDR file failed.

Fix

• crates/media/Cargo.toml: enable the image crate's built-in tga and hdr decoders. These features pull in no new crates, and Cargo.lock is unchanged.
• crates/media/src/lib.rs: add tga and hdr to STILL_EXTENSIONS. A new still_format picks a still's format by its signature and falls back to the extension, because Targa has no signature. probe_bytes and MediaPool decoding both use it.
• Radiance HDR decodes as 32-bit linear float and is sRGB-encoded like OpenEXR, so values above 1 are kept. Targa alpha comes in as straight alpha and goes through the existing unlabeled-alpha interpretation on import, as in After Effects.
• crates/ui-egui/src/menus.rs: the File ▸ Import dialog filter now offers tga and hdr.
• The gap Never crash: media crate without expect() #17 row and the Targa / Radiance rows in file-format-parity.md are updated.

Tests

New tests in crates/media/tests/footage.rs. Both fail without this change.

• targa_still_matches_ffmpeg: ffmpeg encodes an RLE Targa with an alpha gradient. Our decode must be pixel-identical to the source PNG, the footage must be a still with straight alpha and codec TGA, and truncated files (hostile input) must be refused or decoded without panicking.
• radiance_hdr_still_is_linear_float: a file written by the image encoder checks linear 0.214 → 0.5 and that super-white is kept. A second file from ffmpeg's Radiance encoder (RLE scanlines) must decode to sRGB-encoded mid grey within 0.01.

Gates

• cargo fmt --all --check
• cargo clippy -j 4 -p effectcraft-media -p effectcraft-ui-egui --all-targets -- -D warnings
• cargo test -j 4 -p effectcraft-media (all targets)
• cargo test -j 4 -p effectcraft-ui-egui (all targets)
• cargo check -j 4 -p effectcraft-media --target wasm32-unknown-unknown
• cargo xtask layers

I did not run the full cargo xtask ci locally because the machine is shared.

What remains

• DPX / Cineon is still listed in the Media Browser but refused on import. It needs a small pure-Rust DPX decoder.
• AVI and MXF are listed but not wired (FilmCraft reads MXF).
• Any image imported gets imported as image sequence #431: any image imports as a sequence.
• MP3 audio layer goes silent in preview and export after working earlier; WAV of same sound plays #324: MP3 goes silent.
• There is no Targa or Radiance output.

Note: the one-line change to the import-dialog list in menus.rs touches the same line as #735 and #742. Whichever merges second needs a trivial rebase.

🤖 Generated with Claude Code

[vangel76]

Note: the File ▸ Import extension list in crates/ui-egui/src/menus.rs is also extended by #735 (STL) and #742 (FBX). Whichever of these lands later will get a one-line conflict there (keep all extensions); I'll merge current main into the remaining branches right after each merge.