[lc_ctrl] Untested port interaction combinations in state decode and state transition

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## Description

Coverage analysis identified 7 untested port interaction combinations
across two modules:

**lc_ctrl_state_decode** (3 gaps):
- `lc_state_valid_i=0` with `secrets_valid_i=1`
- `lc_state_valid_i=1` with `lc_state_i` at boundary values
- `secrets_valid_i=0` with `fsm_state_i` in non-idle states

**lc_ctrl_state_transition** (4 gaps):
- `volatile_raw_unlock_i=1` with `trans_cmd_i` at invalid values
- `trans_target_i` at boundary values combined with `dec_lc_state_i=0`
- `lc_cnt_i` at maximum value during transition
- `trans_cmd_i` issued with `fsm_state_i` in error state

## Impact

These input combinations have never been exercised in the verification
suite. Bugs on these paths would not be caught by regression.

## Suggested Fix

Add directed tests for each combination listed above.

Locate the verification tests for lc_ctrl_state_decode and lc_ctrl_state_transition and read their existing coverage patterns. Add directed tests for the seven listed combinations, then run the relevant regression and confirm coverage closes for each gap.

Written by the indexing model from the issue text.