* feat(providers): bundle metadata and icons for the 0.61.0 registry

Add the five providers official CodexBar 0.61.0 adds to the registry:
nous (Nous Portal), muse (Muse Code), coderabbit (CodeRabbit),
replicate (Replicate), and huggingface (Hugging Face). Each gets the
bundled metadata the existing registry has: an SVG icon mask, brand
color, dashboard link, status link where upstream defines one,
documentation path, CLI aliases, and a fallback display name.
Metadata mirrors the upstream v0.61.0 provider descriptors and docs;
the registry IDs and display names were verified in the 0.61.0 Linux
probe recorded in the parity review.

The provider icon check now requires the five icons, the catalog
checks pin their identity entries, and QtTests cover the new keys,
aliases, and colors. README and the usage guide describe the 74
provider registry instead of listing the five as not bundled yet, the
completed TODO entry is removed, translation catalogs gain the five
unchanged provider names, and the changelog records the addition.

* fix(providers): use official brand marks for the 0.61.0 icons

Replace the three placeholder glyphs inherited from upstream with the
vendors' official marks: the CodeRabbit rabbit, the Hugging Face face,
and the Replicate steps, sourced from the official monochrome paths
distributed by Simple Icons (CC0). Muse keeps the official Meta glyph
and Nous keeps the upstream CodexBar monogram, since the only official
Nous assets are the mascot illustration and the wordmark, neither of
which reduces to a monochrome 24px mask.

NOTICE.md no longer claims every icon comes from CodexBar.