feat: Represent session game outcome as win/loss/draw

[Amund211]

Summary

Replaces the Won bool on session-detail game results with a three-state
GameOutcome enum (win / loss / draw). Draws are rare but do happen in
Bedwars; today they are silently miscounted as losses because Wins doesn't
increment.

Changes

• domain.GameResult.Won bool → Outcome GameOutcome (win/loss/draw), a
  new enum mirroring the existing domain.Gamemode pattern.
• Outcome is derived from the Wins/Losses deltas in buildGameSegment (the
  Losses counter was previously never read). Added a validation guard
  rejecting impossible single-game movement (deltas outside {0,1}, or both
  win and loss advancing), consistent with the existing FinalDeaths/BedsLost
  guard → falls back to Game: nil.
• Wire/API change in session-at: "won": bool becomes
  "outcome": "win" | "loss" | "draw", with a new
  gameOutcomeToRainbowOutcome converter.
• Tests updated to assert outcomes; added draw and invalid-delta cases.

Detection assumption

A draw is treated as "one game played, but neither Wins nor Losses
incremented". This relies on a draw still advancing GamesPlayed by 1 while
crediting neither counter (otherwise it's filtered out upstream as a non-game).
The enum modeling is correct regardless, but worth confirming against real draw
data if any exists.

⚠️ Downstream consumers

This changes the session-at JSON contract (won → outcome). Rainbow PR
#256 must be updated to work with this updated schema:
Amund211/rainbow#256

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR updates session game results to model the outcome as a three-state enum (win/loss/draw) instead of a boolean, and wires that through the session-at JSON response to correctly represent rare draw games.

Changes:

• Replace domain.GameResult.Won bool with domain.GameOutcome (Outcome field).
• Derive outcome from per-game Wins/Losses deltas in buildGameSegment, including validation that rejects impossible deltas (falls back to Game: nil).
• Update session-at response schema from "won": bool to "outcome": "win" | "loss" | "draw", plus updated tests (including draw + invalid-delta cases).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/domain/game_result.go	Introduces GameOutcome enum and updates GameResult to use Outcome.
internal/app/session_at.go	Computes Outcome from wins/losses deltas and validates impossible single-game movements.
internal/app/session_at_test.go	Updates assertions to outcomes and adds coverage for draw + invalid win/loss delta scenarios.
internal/ports/rainbow_converters.go	Adds gameOutcomeToRainbowOutcome converter for stable JSON contract strings.
internal/ports/session_at.go	Updates session-at wire format to emit outcome and performs conversion.
internal/ports/session_at_test.go	Updates handler tests to expect outcome instead of won.