feat(allowlist): add Shader Languages support

[wakqasahmed]

Summary

• Add .glsl, .hlsl, .wgsl, .metal to the supported file types allowlist
• No default exclude pattern added — shader source files have no conventional test-directory layout shared across GLSL/HLSL/WGSL/Metal toolchains, so allowed_ext_test.go documents this explicitly (matching the existing Prisma precedent)
• Add internal/config/rules/rule_docs/shader.md, a shared shader review rule doc covering precision/NaN propagation, texture and buffer bounds safety (including non-uniform control flow around texture sampling and compute writes), cross-stage binding/layout contracts (std140/std430, register/space, @binding/@group), compute-shader synchronization (barriers, race conditions), GPU performance anti-patterns (dynamic branching, texture-dependent reads), and security/portability concerns (untrusted buffer indices, vendor-specific intrinsics without fallback)
• Register **/*.{glsl,hlsl,wgsl,metal} -> shader.md in system_rules.json
• Add test coverage: allowed-extension matching (all four extensions, case-insensitive), non-exclusion of shader files, and rule resolution

Part of the language-allowlist expansion tracked in #470.

Closes #974

Test plan

• go test ./internal/config/allowlist/... -run 'TestIsAllowedExt|TestIsExcludedPath' -v — PASS
• go test ./internal/config/rules/... -run TestResolve_DefaultRules -v — PASS
• gofmt -s -l . — clean
• go vet ./internal/config/... — clean
• go run scripts/verify-english-only.go — clean (423 files scanned, no unapproved non-English text)

[github-actions]

✅ OpenCodeReview: Review complete: 0 finding(s) across 2 selected item(s).

[wu21-web]

Site documentation updates missing, update at pages/src/content/docs/<locale>/review-rules.md.

[wakqasahmed]

@wu21-web Thanks for the catch — docs added in the latest commit. Updated pages/src/content/docs/{en,ja,ru,zh}/review-rules.md with a row for the new **/*.{glsl,hlsl,wgsl,metal} → shader.md mapping, mirroring the format used for the Elm entry (#978).

Note: the ja/ru/zh translations are my best effort — please have a native speaker double-check the phrasing before merge.

[wu21-web]

@wakqasahmed I will review jp and zh for you, but please reslove the merge conflicts first.

[wakqasahmed]

@wu21-web Resolved — rebased onto latest main and merged, fixing the conflicts in supported_file_types.json, system_rules.json, the two allowlist/rules test files, and all four locale review-rules.md docs (they were conflicting with the recently-merged jsonnet/zig/thrift/capnp entries). Ready for the ja/zh review whenever you get a chance.

[wu21-web]

Approved. Why did you say "the ja/ru/zh translations are my best effort" 🤔 , they didn't need a review really. Good job though.

[wakqasahmed]

Hi @wu21-web — just checking in on this one, it's been about 5 days with CI green and mergeable. Is there anything needed from our side to help move it forward, or any rough idea on timing? No rush, just following up. Thanks for the review!

[wu21-web]

@wakqasahmed Merge conflicts, please rebase branch main.

If you don't want to rebase from time to time, you can add me as a collaborator, and I will keep the branch up to date for you.

[wakqasahmed]

@wu21-web Rebased again — merged latest main and resolved conflicts in supported_file_types.json, allowed_ext_test.go, and system_rules.json (they were conflicting with the newly-merged Solidity/Vyper allowlist entries). Ran go test on the allowlist and rules packages, both green. Should be conflict-free now.