test: improve code coverage across packages

[sunba91-su]

Description

Increase test coverage to ensure reliability and catch regressions. Current baseline measured from CI runs.

Current Coverage

Package	Coverage	Target
internal/commands	74.4%	80%+
internal/convstate	97.6%	95%+ (maintain)
internal/store	43.0%	70%+
internal/config	No tests	50%+
internal/rocket	No tests	50%+

Acceptance Criteria

• internal/config — test config loading, env var parsing, error cases
• internal/store — test edge cases (empty DB, concurrent access, missing sessions)
• internal/commands — test remaining command handlers, permission checks
• internal/rocket — mock WebSocket/REST for client unit tests (or document why untestable)
• Overall project coverage >= 65%
• Coverage report added to CI (optional: re-enable -cover flag once covdata issue is resolved)

Notes

• -cover flag removed from CI due to covdata conflict with -race on Go 1.22 runner; coverage must be verified locally until a fix is available
• Focus on meaningful tests (edge cases, error paths), not just LOCs covered