[codex] Improve FastaGuard discoverability

[ehsanestaji]

Summary

• Add a clearer first-screen README explanation for what FastaGuard does, when to run it, and what it does not replace.
• Make the install section honest about the current state: GitHub release is v0.3.0, while Bioconda/BioContainers remain v0.2.0 until the Bioconda update merges.
• Add v0.3 evidence/release links and update the adoption test to protect the new public positioning.

GitHub metadata updated directly

• Added repository description.
• Added discovery topics: bioinformatics, fasta, fasta-qc, genomics, genome-assembly, quality-control, rust, command-line-tool, nextflow, snakemake, multiqc, bioconda, biocontainers.

Test Plan

• python3 -m unittest discover tests/python -v
• cargo fmt --check
• cargo test --locked
• cargo clippy --locked --all-targets --all-features -- -D warnings
• git diff --check
• trailing whitespace scan

Packaging state

• Bioconda PR Update fastaguard to 0.3.0 bioconda/bioconda-recipes#65816 is still open with all visible checks passing and no maintainer comments.