First pass at full refactor to 2.0 design

Restructures the game around the cyclical run loop from Game Design Doc V2:
5 waves = a cycle, 3 cycles = a phase, each phase ends in a boss.

- New TD.Gameplay.Waves: WaveGroup / PhaseDefinition / RunDefinition author the
  run as draggable weighted pools; RunState owns phase/cycle position, the drawn
  wave slots, and the per-slot enemy buff sets. WaveManager's flat wave array is
  gone -- it now only runs the encounter RunState points at.
- New TD.Gameplay.EnemyUpgrades: the post-wave enemy-buff vote, with public
  live-replicated ballots so the HUD can show who voted for what.
- Inter-wave flow is now strictly sequential: draft -> vote -> build, each stage
  ending early once every player has acted.
- Enemy abilities inverted from per-instance random rolls to deterministic,
  stacking per-wave-slot sets. Six cards ship: Split (reworked), Flight, Blink,
  No Bounty, Gold Theft, Double Up.
- Tower upgrades are a two-step tree: a draft pick unlocks a node, gold converts
  an already-placed tower in place.
- Boss encounters flag their enemies and drive a boss HP bar.
- Player cap reduced to 3 via MatchRules.MaxPlayers.
- GoldConfig is now keyed by global encounter number rather than wave index.

Compiles clean; NOT yet verified in-engine. Editor wiring still required --
see Docs/2.0_Setup_Checklist.md.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Assets/_Project/Scripts/Gameplay/Waves/WaveGroup.cs

@@ -0,0 +1,69 @@
+// Assets/_Project/Scripts/Gameplay/Waves/WaveGroup.cs
+using System;
+using UnityEngine;
+using TD.Core;
+
+namespace TD.Gameplay.Waves
+{
+    /// <summary>
+    /// One weighted candidate inside a <see cref="WaveGroup"/>: a wave that may be drawn,
+    /// and how likely it is to be drawn relative to the group's other entries.
+    /// </summary>
+    /// <remarks>
+    /// <b>Weight is RELATIVE, not an absolute probability.</b> The draw normalizes every
+    /// candidate's weight against the summed weight of the whole candidate set, so three
+    /// entries at 1.0 each are equally likely (33% apiece) and an entry at 0.5 is half as
+    /// likely to be drawn as one at 1.0. This is what makes the default sane: new entries
+    /// start at 1.0, so adding a wave to a group never silently re-weights the others.
+    ///
+    /// <para>A class rather than a struct specifically so <see cref="Weight"/> can carry a
+    /// field initializer — Unity runs it when the inspector creates a fresh array element,
+    /// which is what gives new entries their equal-by-default weighting. Mirrors
+    /// <see cref="WaveGoldEntry"/>.</para>
+    /// </remarks>
+    [Serializable]
+    public class WavePoolEntry
+    {
+        [Tooltip("The wave that may be drawn from this group.")]
+        public WaveDefinition Wave;
+
+        [Tooltip("Relative draw weight within this group's pool. Entries at equal weight are " +
+                 "equally likely; an entry at 0.5 is half as likely as one at 1.0. NOT an " +
+                 "absolute percentage.")]
+        [PoolWeight("wave")]
+        public float Weight = 1f;
+    }
+
+    /// <summary>
+    /// A named, reusable bag of candidate waves. Groups are the unit designers move between
+    /// phases: dragging a group asset from Phase 1's pool to Phase 2's moves every wave in it
+    /// (and their weights) in one action.
+    /// </summary>
+    /// <remarks>
+    /// <b>Why weights live on the entry, not on <see cref="WaveDefinition"/>.</b> Weight is a
+    /// property of "how common is this wave <i>in this pool</i>", not of the wave itself. Keeping
+    /// it here means the same <see cref="WaveDefinition"/> asset can be a staple of one group and
+    /// a rarity in another, and a group carries its tuning with it when moved between phases.
+    ///
+    /// <para><b>Boss groups use the same type.</b> A boss wave is just a
+    /// <see cref="WaveDefinition"/> whose entries spawn a single powerful enemy, so boss pools
+    /// are ordinary <see cref="WaveGroup"/>s referenced from
+    /// <see cref="PhaseDefinition.BossGroups"/>.</para>
+    /// </remarks>
+    [CreateAssetMenu(fileName = "WaveGroup", menuName = "TD/Run/Wave Group", order = 10)]
+    public class WaveGroup : ScriptableObject
+    {
+        [Tooltip("Designer-facing name for this group, shown in run-structure validation " +
+                 "messages. Falls back to the asset name when empty.")]
+        public string DisplayName;
+
+        [Tooltip("Candidate waves in this group, each with a relative draw weight.")]
+        public WavePoolEntry[] Waves;
+
+        /// <summary>Name used in validation and log messages. Falls back to the asset name.</summary>
+        public string Label => string.IsNullOrWhiteSpace(DisplayName) ? name : DisplayName;
+
+        /// <summary>Number of entries, including any that are null or zero-weight.</summary>
+        public int Count => Waves?.Length ?? 0;
+    }
+}