fix(#825): remove dead defaults.auto_merge config field

[fullsend-ai-coder]

Summary

• Remove the dead defaults.auto_merge config field (RepoDefaults.AutoMerge) which was declared, defaulted, parsed, and tested but never consumed to gate any merge behavior
• Clean up references across Go structs/tests, web admin TypeScript types, YAML fixtures, and ADR 0045
• Existing config.yaml files containing auto_merge continue to parse without error (yaml.v3 silently ignores unknown keys)

Test plan

• Go tests pass for internal/config (95.5% coverage) and internal/layers (84.9% coverage)
• go vet passes on affected packages
• Secret scan passes on all modified files
• TypeScript tests (vitest) — not runnable in sandbox (no node_modules); changes are trivial fixture updates
• Pre-commit — not runnable in sandbox (network-restricted); deferred to post-script

---

Closes #825

Post-script verification

• Branch is not main/master (agent/825-remove-dead-auto-merge)
• Secret scan passed (gitleaks — c887fc47c59d8b87b5282ca44044d2933d30df41..HEAD)
• PR body secret scan passed (gitleaks — no-git)
• Pre-commit hooks passed (authoritative run on runner)
• Tests ran inside sandbox

[fullsend-ai-review]

🤖 Finished Review · ✅ Success · Started 8:59 AM UTC · Completed 9:11 AM UTC
Commit: 205f1d5 · View workflow run →

[fullsend-ai-review]

Looks good to me

Previous run

Looks good to me

[guyoron1]

/fs-fix

[fullsend-ai-coder]

🤖 Finished Fix · ✅ Success · Started 10:31 AM UTC · Completed 10:36 AM UTC
Commit: 205f1d5 · View workflow run →

[fullsend-ai-coder]

🔧 Fix agent — iteration 1 (human-triggered)

Addressed 1 review finding: removed stray blank lines in enrollment_test.go YAML fixtures left after auto_merge field removal.

Fixed (1):

1. test-data-formatting: blank lines left in test YAML after removing auto_merge (internal/layers/enrollment_test.go): Removed blank lines at lines 237 and 307 between max_implementation_retries and agents keys, matching the formatting of other YAML fixtures in this PR

Tests: passed

Next steps:

• /fs-review — request a re-review of the changes
• /fs-fix <your instruction> — run another fix pass with specific guidance
• Push commits directly — review re-runs automatically on push
  _{Updated by fullsend fix agent}

[fullsend-ai-review]

🤖 Finished Review · ✅ Success · Started 10:40 AM UTC · Completed 10:51 AM UTC
Commit: 89d78f0 · View workflow run →

[github-actions]

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