feat(allowlist): expand supported file types — language experts wanted

## Description

OpenCodeReview currently supports **71 file extensions** for code review. However, many popular and emerging languages are missing from the allowlist. We're looking for **language experts** to help add proper support for their favorite languages — including file extensions, test-file exclude patterns, and **language-specific review rules**.

This is a **tracking issue**. Pick a language group below, create a sub-issue referencing this one, and submit a PR. Each language group is independent and can be contributed separately.

## Currently Supported

71 extensions (click to expand)

`.java` `.kt` `.kts` `.scala` `.groovy` `.py` `.pyi` `.js` `.jsx` `.ts` `.tsx` `.mjs` `.cjs` `.c` `.h` `.cpp` `.cc` `.cxx` `.hpp` `.hxx` `.cs` `.vb` `.fs` `.go` `.rs` `.rb` `.rake` `.gemspec` `.php` `.swift` `.m` `.mm` `.sh` `.bash` `.zsh` `.fish` `.ps1` `.sql` `.css` `.scss` `.sass` `.less` `.html` `.htm` `.ftl` `.ftlh` `.ftlx` `.astro` `.vue` `.svelte` `.xml` `.yaml` `.yml` `.json` `.toml` `.ini` `.env` `.gradle` `.cmake` `.r` `.lua` `.pl` `.pm` `.ex` `.exs` `.erl` `.hrl` `.ets` `.json5` `.dart` `.tf`

## Wanted — Language Groups

Pick one (or more!) and open a sub-issue:

| Language Group | Extensions | Test Exclude Patterns Needed | Difficulty |
|---|---|---|---|
| **Zig** | `.zig` | `**/test/*.zig`, `**/*_test.zig` | ★☆☆ |
| **Nim** | `.nim`, `.nims`, `.nimble` | `**/tests/**/*.nim` | ★☆☆ |
| **Haskell** | `.hs`, `.lhs` | `**/test/**/*.hs`, `**/*Spec.hs` | ★★☆ |
| **Clojure** | `.clj`, `.cljs`, `.cljc`, `.edn` | `**/test/**/*.clj` | ★★☆ |
| **Elm** | `.elm` | `**/tests/**/*.elm` | ★☆☆ |
| **OCaml / ReasonML** | `.ml`, `.mli`, `.re`, `.rei` | `**/test/**/*.ml` | ★★☆ |
| **Protocol Buffers & gRPC** | `.proto` | — | ★☆☆ |
| **GraphQL** | `.graphql`, `.gql` | — | ★☆☆ |
| **Solidity / Web3** | `.sol`, `.vy` | `**/test/**/*.sol`, `**/*.t.sol` | ★★☆ |
| **Move** | `.move` | `**/tests/**/*.move` | ★☆☆ |
| **HCL / Terraform** | `.hcl`, `.tfvars` (`.tf` already supported) | — | ★☆☆ |
| **Nix** | `.nix` | — | ★☆☆ |
| **Dhall** | `.dhall` | — | ★☆☆ |
| **Jsonnet** | `.jsonnet`, `.libsonnet` | — | ★☆☆ |
| **Bicep** | `.bicep` | — | ★☆☆ |
| **Prisma** | `.prisma` | — | ★☆☆ |
| **Thrift / Cap'n Proto** | `.thrift`, `.capnp` | — | ★☆☆ |
| **Shader Languages** | `.glsl`, `.hlsl`, `.wgsl`, `.metal` | — | ★★☆ |
| **Template Engines** | `.pug`, `.haml`, `.slim`, `.erb`, `.twig`, `.jinja2`, `.j2`, `.hbs`, `.mustache`, `.tera` | — | ★★☆ |
| **Hardware Description** | `.v`, `.sv`, `.vhd`, `.vhdl` | `**/tb_*.v`, `**/*_tb.v` | ★★☆ |
| **Julia** | `.jl` | `**/test/**/*.jl` | ★☆☆ |
| **Crystal** | `.cr` | `**/spec/**/*_spec.cr` | ★☆☆ |
| **V (vlang)** | `.v`, `.vsh` | `**/tests/**/*.v`, `**/*_test.v` | ★☆☆ |
| **Mojo** | `.mojo`, `.🔥` | — | ★☆☆ |

> 💡 Don't see your language? Comment below to propose it!

## Scope

- File(s):
- `internal/config/allowlist/supported_file_types.json` — add extensions
- `internal/config/allowlist/default_exclude_patterns.json` — add test patterns (if applicable)
- `internal/config/allowlist/allowed_ext_test.go` — add test cases
- `internal/config/rules/rule_docs/.md` — **(recommended)** language-specific review rules
- `internal/config/rules/system_rules.json` — register path-to-rule mapping
- Function/area: `allowedext` package + `rules` subsystem

## How to Contribute

1. **Comment below** claiming a language group (to avoid duplicate work)
2. **Create a sub-issue** titled `feat(allowlist): add support` referencing this issue
3. **Submit a PR** with:
- Extensions added to `supported_file_types.json`
- Test exclude patterns added to `default_exclude_patterns.json` (if the language has conventional test file locations)
- Test cases added to `allowed_ext_test.go` covering both `IsAllowedExt` and `IsExcludedPath`
- **(Recommended)** A review rule doc `internal/config/rules/rule_docs/.md` with language-specific review focus areas (see existing examples like `rust.md`, `python.md`, `java.md` for format and depth)
- **(Recommended)** Register the glob-to-rule mapping in `internal/config/rules/system_rules.json`
4. Ensure `make test` and `make check` pass

### Review Rule Doc Guidelines

Review rule docs define what OCR should focus on when reviewing code in that language. A good rule doc covers:

- **Common correctness pitfalls** (e.g., ownership bugs in Rust, null safety in Kotlin)
- **Error handling idioms** specific to the language
- **Concurrency & async patterns** and their foot-guns
- **Performance anti-patterns** common in the ecosystem
- **Security-sensitive areas** (injection, unsafe operations, crypto misuse)
- **Type/API design conventions** valued by the community

See `internal/config/rules/rule_docs/rust.md` or `python.md` for reference. Your language expertise is exactly what makes these rules valuable — generic rules already exist in `default.md`.

## Acceptance Criteria (per sub-PR)

- [ ] Extensions added to `supported_file_types.json`
- [ ] Test exclude patterns added if the language has well-known test conventions
- [ ] Test cases cover both positive (extension recognized) and negative (test files excluded) scenarios
- [ ] (Recommended) Rule doc added at `internal/config/rules/rule_docs/.md`
- [ ] (Recommended) Path mapping registered in `internal/config/rules/system_rules.json`
- [ ] `make test` passes
- [ ] `make check` passes

## Context

**Allowlist**: uses a simple JSON array of extensions with case-insensitive matching. The exclude patterns use [doublestar](https://github.com/bmatcuk/doublestar) glob syntax supporting `**` (recursive), `*` (single-segment), and `{a,b}` (brace expansion).

**Review rules**: `system_rules.json` maps file glob patterns to rule doc filenames. When OCR reviews a file matching a pattern, the corresponding rule doc is injected into the LLM prompt to guide the review. Files not matching any specific pattern fall back to `default.md`.

Adding a language is a great way to make your first contribution. Language expertise helps ensure the test patterns match real-world project conventions and the review rules capture genuine pitfalls — not just generic advice.

Choose one language group and create a sub-issue before changing the allowlist. Start with internal/config/allowlist/supported_file_types.json, default_exclude_patterns.json, and allowed_ext_test.go; review matching rule examples under internal/config/rules/rule_docs/. Done means the extension and applicable exclusions have positive and negative tests, and make test plus make check pass.

Written by the indexing model from the issue text.