feat(app): water temp + current-strength gauge on Today (v0.4.2)

Surfaces the new /api/current data on the Today screen, covering the
backlog 수온 + 조류세기 items the user asked for:
- Weather card gains a marine line: 🌡 수온 (1-decimal) and 🌀 조류 in knots
  with a 16-point Korean compass direction.
- Current-strength gauge (% of the day's max current, accent->gold bar) like
  the reference app's "37%". Today uses the current hour; other days noon.
- types/api mirror MarineDay/MarineHour; data fetched per spot+date and
  hidden silently if the (unofficial) endpoint fails.

Verified on a mobile viewport: 군산 shows 수온 21.1℃ · 조류 0.9kn 서 · 조류세기 85%.

Constraint: water temp/current are KHOA model forecast, not observation; the section self-hides on failure so it never blocks the core tide view.
Confidence: high
Scope-risk: module
Reversibility: trivial
Directive: If users want it, add a water-temp line to the 바다날씨 chart next; label model-sourced values clearly.
Tested: app build clean; APK deployed (v0.4.2); Playwright mobile screenshot confirms the marine line + gauge render.
Not-tested: on-device; accuracy of model current direction vs observation.
Related: docs/BACKLOG.md 2/4

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