Add Dependabot auto-merge workflow for dependency updates

[Claude]

Implements automatic merging of Dependabot PRs when all CI checks pass.

Changes

• New workflow: .github/workflows/dependabot-auto-merge.yml
  • Triggers on CI workflow completion
  • Verifies PR author is dependabot[bot]
  • Auto-approves and enables auto-merge when all checks pass
  • Uses squash merge method
  • Falls back to direct merge if auto-merge unavailable

Behavior

When Dependabot opens a PR:

1. CI runs (lint, test, build)
2. On success, workflow auto-approves the PR
3. Enables GitHub auto-merge to merge when requirements met
4. PR merges to main automatically

Requires contents: write and pull-requests: write permissions.

[github-actions]

Test Results (Linux 3.14)

483 tests  ±0   483 ✅ ±0   42s ⏱️ +2s
  1 suites ±0     0 💤 ±0 
  1 files   ±0     0 ❌ ±0 

Results for commit ed5694f. ± Comparison against base commit 2870f3b.

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.97%. Comparing base (2870f3b) to head (ed5694f).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #56   +/-   ##
=======================================
  Coverage   87.97%   87.97%           
=======================================
  Files          17       17           
  Lines        2736     2736           
=======================================
  Hits         2407     2407           
  Misses        329      329           

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