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/Core/PoolWeightAttribute.cs

@@ -0,0 +1,35 @@
+// Assets/_Project/Scripts/Core/PoolWeightAttribute.cs
+using UnityEngine;
+
+namespace TD.Core
+{
+    /// <summary>
+    /// Marks a float field as a 0–1 <b>relative</b> draw weight inside an authored pool. The
+    /// inspector renders it as a slider and, when the value is zero, shows a warning directly
+    /// beneath explaining that the entry can never be drawn.
+    /// </summary>
+    /// <remarks>
+    /// <b>Relative, not absolute.</b> Weights are normalized against the summed weight of the
+    /// candidate set at draw time, so entries at equal weight are equally likely and an entry at
+    /// 0.5 is half as likely as one at 1.0. This is why every weight field defaults to 1 —
+    /// adding an entry to a pool then never silently re-weights the entries already in it.
+    ///
+    /// <para><b>The warning is advisory.</b> Muting an entry while tuning is a legitimate
+    /// workflow, so the drawer never clamps the value or blocks the edit. It exists because a
+    /// zero-weight entry is otherwise indistinguishable, in play, from one that simply hasn't come
+    /// up yet — the failure is silent, so the authoring surface has to be loud.</para>
+    /// </remarks>
+    public class PoolWeightAttribute : PropertyAttribute
+    {
+        /// <summary>
+        /// Noun used in the zero-weight warning ("this <c>wave</c> can never be drawn"). Keep it
+        /// singular and lowercase.
+        /// </summary>
+        public readonly string Noun;
+
+        public PoolWeightAttribute(string noun = "entry")
+        {
+            Noun = string.IsNullOrWhiteSpace(noun) ? "entry" : noun;
+        }
+    }
+}