Add ESLint rule to enforce "pull request" over "PR" in user-facing strings

[Copilot]

This PR adds a custom ESLint rule no-pr-in-user-strings that detects usage of "PR" in user-facing strings and enforces the use of "pull request" instead for better accessibility and consistency.

Implementation

The rule implements the following functionality:

• Detects "PR" in localized strings: Checks string literals passed to vscode.l10n.t() and l10n.t() calls
• Word boundary matching: Uses /\bPR\b/ regex to match "PR" as a standalone word, avoiding false positives like "APRICOT"
• Clear error messaging: Provides helpful error message suggesting "pull request" instead of "PR"
• Error-level enforcement: Configured as an error to prevent commits with violations

Files Added/Modified

• NEW: build/eslint-rules/no-pr-in-user-strings.js - The ESLint rule implementation
• MODIFIED: build/eslint-rules/index.js - Export the new rule
• MODIFIED: .eslintrc.js - Configure rule as error level for TypeScript files
• MODIFIED: src/issues/issueFeatureRegistrar.ts - Fix existing violation

Example Usage

The rule catches cases like:

// ❌ This will trigger an error
const message = vscode.l10n.t('Creating PR failed');

// ✅ This is correct
const message = vscode.l10n.t('Creating pull request failed');

// ✅ This won't trigger (not in l10n call)
const debug = 'PR debugging info';

// ✅ This won't trigger (PR not standalone)
const fruit = vscode.l10n.t('APRICOT is delicious');

Validation

The rule successfully detected and helped fix 1 existing violation in the codebase:

• Before: @githubpr Summarize PR {0}/{1}#{2}
• After: @githubpr Summarize pull request {0}/{1}#{2}

All existing lint rules continue to work, and both npm run lint and npm run hygiene pass successfully.

Created from VS Code via the GitHub Pull Request extension.

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