feat(levels): c50c trades one good idea repeated for five that alternate

c50b is sealed where it stands, as a reference sample rather than a candidate.
Its packed construction was judged good — clearing a board from the rim inward
is the experience it proved out — but at 32 of 50 levels it played as one level
fifty times: 体验太单一了，因为基本都是满盘. The note on why it is kept lives at
the top of its module, because the lesson is the useful part.

It was monotonous on a second axis nobody asked about. 环绕 and 花瓣, the two
route families the brief singles out as the good-looking ones, were absent from
it entirely — not by choice but by a crossing threshold. At 1.0 crossings per
cell, 0% of orbits boards pass and 4% of spirals; at 1.2, 84% and 94% do. The
gate meant to answer "交叉点太多" had quietly deleted the families most worth
looking at, so it moves to 1.2 — still half the 2.36 that drew the complaint.

c50c alternates five kinds of level every three to five: packed boards down to
32%, long-route departures to watch, deep locks to solve, small quick boards,
and segments given over to orbits, petals and spirals by name. All six families
appear, no family exceeds 24%, and the plan is 13 segments rather than 9.

Selection learned to ask for variety outright — by family, piece count and
longest drawn route — instead of hoping it falls out of a difficulty score.

Rule bot across all three: 50/50 cleared and zero dead taps everywhere; c50c
sits between the other two on blind rotations and on how much there is to do.

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

levels/plan-c50b.json

@@ -1,11 +1,93 @@
 [
- { "name": "起步 · 小满盘", "count": 6, "packed": true, "maxCells": 37 },
- { "name": "深锁初见", "count": 4, "rotations": [3], "packed": false, "maxDensity": 0.28 },
- { "name": "满盘 · 由外向内", "count": 7, "packed": true },
- { "name": "变奏 · 深一点", "count": 5, "rotations": [4, 5], "packed": false },
- { "name": "大满盘", "count": 7, "packed": true, "minCells": 61 },
- { "name": "中段 · 稀而绕", "count": 4, "rotations": [3], "packed": false, "maxDensity": 0.30 },
- { "name": "满盘 · 转得更深", "count": 6, "packed": true, "minRotations": 3 },
- { "name": "收束前的深锁", "count": 5, "rotations": [4, 5], "packed": false },
- { "name": "终章 · 最满的几盘", "count": 6, "packed": true, "minFill": 1 }
-]
+ {
+  "name": "开场 · 小满盘",
+  "count": 4,
+  "packed": true,
+  "maxCells": 37
+ },
+ {
+  "name": "长路线演出",
+  "count": 5,
+  "packed": false,
+  "maxPieces": 14,
+  "minLongestRoute": 30
+ },
+ {
+  "name": "深锁初见",
+  "count": 4,
+  "rotations": [
+   3,
+   4
+  ],
+  "packed": false
+ },
+ {
+  "name": "环绕 · 同心圈",
+  "count": 3,
+  "families": [
+   "orbits"
+  ]
+ },
+ {
+  "name": "花瓣 · 回到花心",
+  "count": 3,
+  "families": [
+   "petals"
+  ]
+ },
+ {
+  "name": "满盘 · 由外向内",
+  "count": 2,
+  "packed": true
+ },
+ {
+  "name": "紧凑快节奏",
+  "count": 4,
+  "packed": false,
+  "maxPieces": 13,
+  "maxCells": 37
+ },
+ {
+  "name": "深锁 · 四转",
+  "count": 5,
+  "rotations": [
+   4,
+   5
+  ],
+  "packed": false
+ },
+ {
+  "name": "大盘长路线",
+  "count": 4,
+  "packed": false,
+  "minCells": 61,
+  "minLongestRoute": 40
+ },
+ {
+  "name": "满盘 · 转得更深",
+  "count": 5,
+  "packed": true,
+  "minRotations": 3
+ },
+ {
+  "name": "螺旋",
+  "count": 3,
+  "families": [
+   "spiral"
+  ]
+ },
+ {
+  "name": "交织收束",
+  "count": 3,
+  "families": [
+   "crossing",
+   "weave"
+  ]
+ },
+ {
+  "name": "终章 · 全满收束",
+  "count": 5,
+  "packed": true,
+  "minFill": 1
+ }
+]