Add Mojo language wiring

[aaiyer]

Summary

Adds the missing Mojo language wiring now that a Mojo tree-sitter grammar is vendored in the C backend.

Root Cause

The repository includes tree_sitter_mojo, but the language was not reachable through the normal discovery/indexing path:

• no CBM_LANG_MOJO enum entry
• no .mojo extension mapping
• no user config language-name mapping
• no CBMLangSpec row for Mojo parser/query node types

As a result, .mojo files did not produce Mojo symbols during indexing.

Changes

• Adds CBM_LANG_MOJO.
• Maps .mojo files to Mojo.
• Adds mojo to user-config language name lookup.
• Wires the vendored tree_sitter_mojo parser into lang_specs with function, class/trait, call, import, branch, assignment, and module node types.
• Adds language-extension and grammar-regression coverage.

Validation

build/c/test-runner language grammar_regression

Result: 218 passed.

I also verified the patched backend against a small .mojo sample locally: it indexed fn, struct, and method symbols, and outbound trace found a method calling a top-level function.

[DeusData]

Thanks for picking up Mojo wiring. Triage: draft language-support PR, backlog priority.

Before review can proceed, please remove or fully justify the unrelated vendored/nomic/code_vectors_blob.S change. Mojo language wiring should not include an unrelated vendored/generated blob. Once that is gone, review can focus on the expected pieces: extension mapping, language spec wiring, user-config alias, and grammar regression coverage.