Add Mojo language support

[Tokarzewski]

What does this PR do?

Adds Mojo (Modular's Python-superset systems language) as the 159th language.

Vendors the lsh/tree-sitter-mojo grammar (forked from tree-sitter-python, MIT, ABI 15, C scanner — no libstdc++) and wires it through the standard language path:

• CBM_LANG_MOJO enum (appended, no renumbering of persisted DBs)
• grammar_mojo.c wrapper + vendored internal/cbm/vendored/grammars/mojo/
• extraction spec in lang_specs.c
• .mojo and .🔥 extensions + LANG_NAMES in language.c

Spec design

The grammar's node types mirror Python's, so the spec reuses the py_* arrays and overrides only the class types (same reuse pattern already used for CFScript→js_*). Mojo-specific divergences:

• fn/def → function_definition
• struct/class → class_definition; trait and __extension get their own nodes (trait_definition / extension_definition), so traits map to the Interface label
• compile-time alias NAME = value has no dedicated grammar node — the upstream grammar recovers it as an assignment (name still captured)

Verification

Indexed real Mojo corpora end-to-end with the resulting binary:

• NuMojo (pure Mojo, 135 files): functions, methods, structs, traits (Interface), decorators, calls, imports all extract; core NDArray struct correctly surfaces as the most-referenced type (in-degree 306).
• EnergyPlusMojo + 7,354 machine-generated Mojo files: 166K+ nodes, no crashes — robust to malformed/partial generated Mojo.

Adds a test_grammar_regression.c case (fn→Function, struct→Class, trait→Interface) and the matching test_grammar_labels.c golden. Updates the grammar MANIFEST.md (recorded as community/unverified — not in nvim-treesitter/Helix registries), THIRD_PARTY.md, new-languages.json, and the README language count.

Checklist

• Every commit is signed off (git commit -s)
• Tests pass locally — grammar_label_goldens, grammar_code_extracts_defs, grammar_imports_extracted, and the 53-language CALLS-breadth check all pass for Mojo. (Unrelated to this PR: test_incremental RSS-budget assertion trips under ASAN, and pre-existing UBSan null-arg warnings in the vendored crystal/rescript/purescript scanners.)
• Lint — clang-format clean on all hand-written files (lang_specs.c, language.c, grammar_mojo.c, tests)
• New behavior covered by a test (regression case + label golden)

Heads-up (not part of this PR): on bleeding-edge GCC 16, src/cli/cli.c:1461 trips -Werror=discarded-qualifiers on a strstr const-discard, which blocks the build regardless of this change. Worth a one-line cast in a separate PR.

🤖 Generated with Claude Code