feat: Add AES-256-GCM encryption utility for Jira credential storage

[Pratikshya32]

Summary

Adds a server-side encryption utility for securely storing Jira API tokens. Credentials are encrypted before database storage and decrypted only when needed.

Changes

• Added src/lib/crypto/credentialEncryption.ts

cc @Priyanshu-byte-coder

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[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[Priyanshu-byte-coder]

This PR has merge conflicts with main. Please rebase:

git fetch origin
git rebase origin/main
# fix conflicts, then:
git push --force-with-lease

[Priyanshu-byte-coder]

This PR cannot be merged because it branches from a significantly outdated version of main and includes ~9400 deletions of code that was already updated separately. The actual feature/fix in this PR is valuable though!

To get your contribution merged:

1. Sync your fork: git fetch upstream && git rebase upstream/main
2. Create a new branch from the updated main: git checkout -b your-feature-name origin/main
3. Cherry-pick or re-apply only your actual changes
4. Open a new focused PR with just your changes

Labeling your contribution for GSSoC scoring.

[Priyanshu-byte-coder]

This PR has merge conflicts with main. Please rebase to unblock it:

git fetch origin
git rebase origin/main
# resolve conflicts, then:
git push --force-with-lease