`LANGUAGE_OVERRIDES` only covered .h, .js, .scm, .ts, and .xml. For every other suffix with multiple candidate grammars, the alphabetically-first one won: .svg/.xsd/.xsl/.xslt/.rng files were parsed with the dtd grammar (rendering garbage), .mli went to ocaml instead of ocaml_interface, .tsv/.psv went to csv, and .tf/tfvars went to hcl. Since a non-None language blocks the Pygments fallback, these file types regressed compared to Pygments-only highlighting. Overrides are now defined for every ambiguous suffix with a clear answer. Suffixes that are genuinely ambiguous (.m, .pp, .cls, .bb, .vsh) return None so Pygments, which has content-based detection, can decide instead. Testing: Added language detection tests for the XML family, OCaml interfaces, delimiter-separated files, Terraform, and the ambiguous-suffix None behavior. Ran all treesitter and diffviewer tests.