SubMiner advertises subtitle syncing with alass and ffsubsync, but the dedicated test:subtitle command currently does not run any tests. There is already lower-level coverage in src/core/services/subsync.test.ts, but the test matrix and contributor-facing commands do not reflect that reality. This task should replace the no-op lane with real verification, align scripts with the existing subsync test surface, and make the user-facing docs honest about how subtitle sync is verified.
Acceptance Criteria
#1 The test:subtitle entrypoint runs real automated verification instead of echoing a placeholder message.
#2 The subtitle verification lane covers both alass and ffsubsync behavior, including at least one non-happy-path scenario relevant to current functionality.
#3 Contributor-facing documentation points to the real subtitle verification command and no longer implies a dedicated test lane exists when it does not.
#4 The resulting verification strategy integrates cleanly with the repository-wide test matrix without duplicating or hiding existing subsync coverage.
Implementation Plan
Audit the existing subtitle-sync test surface, especially src/core/services/subsync.test.ts, and decide whether test:subtitle should reuse or regroup that coverage.
Replace the placeholder script with a real automated command and keep the matrix legible alongside TASK-87.1 work.
Update README or related docs so the advertised subtitle verification path matches reality.
Verify both alass and ffsubsync behavior remain covered by the resulting lane.