feat(allowlist): add Jinja template support

[dvd233]

Description

Add first-class review support for Jinja template files as the focused subtask tracked in #1055:

• recognize .jinja2 and .j2 files case-insensitively;
• route them to a dedicated Jinja review rule covering escaping contexts, template injection, undefined values, includes/imports/macros, output correctness, and render-time performance;
• test lowercase and uppercase allowlist and rule resolution;
• document the new built-in mapping in all four review-rules locale pages.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring (no functional changes)
• Documentation update
• CI / Build / Tooling

How Has This Been Tested?

• make test passes locally
• Manual testing (described below)

Validation performed on Windows/amd64 with Go 1.27.0, GNU Make 4.4.1, and GCC 16.2.0:

• make check
• make test (all 23 Go packages with -race -count=1)
• make build
• go test -race -count=1 ./internal/config/allowlist ./internal/config/rules
• Pages lint, 32 tests, typecheck, production webpack build, bundle-size check, and HTTP smoke checks for the built site

The repository-required ocr review --audience agent --background "briefly summarize the background requirements" command was attempted, but this local environment has no configured LLM endpoint. I completed a separate standards/spec self-review; both axes reported no remaining findings.

Checklist

• My code follows the project's coding style (go fmt, go vet)
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or my feature works
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly (if applicable)
• I have signed the CLA

Related Issues

Closes #1055

Part of #470

[CLAassistant]

All committers have signed the CLA.

[github-actions]

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

[dvd233]

@wu21-web The requested documentation wording has been shortened in 46d669c, and the review thread has been resolved. Could you please take another look when convenient? Thanks!

[Qiyuanqiii]

The PR description has been flattened into a single Markdown line, so its headings, lists, and checkboxes do not render correctly. Please edit the PR description to restore the intended line breaks and blank lines.

[Qiyuanqiii]

The problem appears like this

[dvd233]

@Qiyuanqiii Fixed — the PR description has been restored with its headings, lists, blank lines, and task checkboxes rendering correctly. The CLA item remains checked. Thanks for catching this!

[Qiyuanqiii]

GitHub Linguist lists .jinja as Jinja’s primary extension. Since this PR is intentionally scoped to .jinja2 and .j2 per #1055, this does not need to block the PR, but it would be useful to track .jinja support in a follow-up issue.

[wu21-web]

@dvd233 Merge conflicts, please rebase main and I will review.

[dvd233]

@wu21-web Rebased onto the latest main (cfbb62e) and resolved the conflicts while preserving both the upstream MATLAB support and this PR's Jinja support. Local validation passed: make check, make test (with -race -count=1), make build, and the Pages lint/test/typecheck/build/size checks. The PR is now conflict-free. Could you please review again? Thanks!

[wu21-web]

Overall this is complete. I would approve this.

[wu21-web]

LGTM

[dvd233]

All review suggestions are addressed and checks are green — this is ready from my side whenever you'd like to merge. Thanks again for the thorough reviews!

[wu21-web]

LGTM