Cover the action entrypoint in Vitest coverage

[kitsuyui]

Summary

Cover the action entrypoint in Vitest coverage

Add a dedicated src/index.spec.ts that imports the action entrypoint under
mocks and exercises the reachable src/index.ts branches for the normal
path, legacy input aliases, invalid max-expected-occurrences, and
downstream failure handling. Make Vitest coverage explicitly include
src/**/*.ts while excluding *.spec.ts so the published coverage report
keeps the action entrypoint visible even when it is only reached through
import-time execution.

Chosen fix

• approach: surface-add-index-spec-and-explicit-coverage-include
  This is the smallest safe plan that fixes the finding at its source: the
  published coverage should represent the real action entrypath. It stays
  within the repo's existing Vitest coverage setup, avoids repository-settings
  changes, does not weaken any quality gate, and does not require a broader
  refactor of action orchestration. Adding only coverage inclusion would
  expose the gap but leave the main path untested; adding only tests would
  cover today's file but still rely on implicit inclusion behavior. Doing
  both keeps the change local and durable.

[github-actions]

🎉 Happy commit!

• dogfooding: PR Cover the action entrypoint in Vitest coverage #853 always celebrates.
• dogfooding: 40e24228113932b91a1d6040f0acca510ac623f1 always celebrates.

[github-actions]

gh-counter

PR gate

	Removed	Added	+/-
TODO/FIXME	0	0	0

Repo dashboard

	main (4ff7c64)	#853 (bb326f1)	+/-
TODO/FIXME	0	0	0

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Reported by gh-counter

[github-actions]

Code Metrics Report

	main (4ff7c64)	#853 (bb326f1)	+/-
Coverage	99.2%	97.6%	-1.7%
Code to Test Ratio	1:1.3	1:1.6	+0.2
Test Execution Time	1s	1s	0s

Details

  |                     | main (4ff7c64) | #853 (bb326f1) |  +/-  |
  |---------------------|----------------|----------------|-------|
- | Coverage            |          99.2% |          97.6% | -1.7% |
  |   Files             |              5 |              7 |    +2 |
  |   Lines             |            134 |            170 |   +36 |
+ |   Covered           |            133 |            166 |   +33 |
+ | Code to Test Ratio  |          1:1.3 |          1:1.6 |  +0.2 |
  |   Code              |            714 |            714 |     0 |
+ |   Test              |            966 |           1180 |  +214 |
  | Test Execution Time |             1s |             1s |    0s |

Code coverage of files in pull request scope (0.0% → 91.6%)

Files	Coverage	+/-	Status
src/index.ts	91.6%	+91.6%	affected

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Reported by octocov