## Description:
Follow-up to #4469.
The Doomsday Clock drains a doomed side's troops but leaves its navy
untouched, so a coastal or island turtle can sit below the bar
indefinitely on warship defense, exactly the stall the clock is meant to
break.
This decays the warships of a flagged (sub-threshold, non-leader) side
on the same ramp as its troops:
- Each warship loses a percentage of its (veterancy-adjusted) max health
per second, reusing `doomsdayClockDrain`, so the fleet and the army
bleed in lockstep and reach zero together (~55s from full at the default
rate).
- Destruction passes **no attacker**, so it routes through
`UnitImpl.delete` as an environmental loss: no kill credit, no
boat-destroy stats, no veterancy granted. Scoring integrity is
preserved.
- Healing is suppressed for a flagged owner
(`WarshipExecution.healWarship` early-returns), so the decay actually
sinks the fleet instead of being out-healed at a port. Inert when the
mode is off, since the mark is never set.
- The leader's fleet is spared, same as its troops.
No new config: warships reuse the existing drain curve. No HUD change,
since warships count as part of the side's forces alongside troops.
Tested: 4 new unit tests (same-ramp decay, no-kill-credit destruction,
leader spared, warn-window grace), the full `DoomsdayClockExecution` and
`Warship` suites, the whole test suite (1784 passing), `build-prod`, and
a headless full-game sim run (resolves cleanly with the decay live,
deterministic).
Zixer1
66063d6178