Fix/legacy api key auth v2

[Bhavy12-cell]

Closes #1635

Fixed legacy API key authentication failure after hash migration.

Root cause:
authenticateApiKey() compared hash against api_key column for legacy
rows, but legacy rows contain plaintext — so the comparison always failed.

Fix:

• Step 1: Try modern hashed lookup (api_key_hash column)
• Step 2: Fallback to plaintext comparison for legacy rows
  (where api_key_hash IS NULL)
• On successful legacy auth, backfill api_key_hash and update
  last_used_at in one update
• New keys no longer store plaintext in api_key column
• Uses maybeSingle() instead of single() to avoid errors on no match

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[Priyanshu-byte-coder]

This PR has conflicts with main. Please rebase on main and resolve conflicts, then we can review.

[Bhavy12-cell]

Hi @Priyanshu-byte-coder!

Rebased on latest main and force-pushed. No conflicts remaining. Ready for review!

[Priyanshu-byte-coder]

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

git fetch origin
git rebase origin/main

[Bhavy12-cell]

Hi @Priyanshu-byte-coder!
Rebased on latest main. Ready for review!