Approve Wu river cavalry handpainted sprite v4

docs/unit-sprite-wu-cavalry-river-v4-approval-packet.md

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+# Wu River Cavalry v4 Approval Packet
+
+- status: approved during continuous production run
+- unit: `unit-wu-cavalry-river`
+- source art: `handpaint-batch4-wu-cavalry-river-source-v1.png`
+- contact sheet: `handpaint-batch4-wu-cavalry-river-v4-contact.png`
+- animation GIF: `handpaint-batch4-wu-cavalry-river-v4-animation.gif`
+- before/after: `handpaint-batch4-wu-cavalry-river-v4-before-after.png`
+- scale compare: `handpaint-batch4-wu-cavalry-river-v4-scale-compare.png`
+- battle composite: `handpaint-batch4-wu-cavalry-river-v4-battle-composite.png`
+- browser check: `handpaint-batch4-wu-cavalry-river-v4-debug-preview-battle-check.png`
+- current board: `unit-sprite-current-approval-board.png`
+- debug URL: `http://127.0.0.1:4173/heros_web/?debug&debugSpritePreview=unit-wu-cavalry-river&v=wu-cavalry-river-v4`
+
+## Visual Decision
+
+Approved for the continuous batch run. v4 replaces the previous boat-like placeholder with a readable mounted Wu river cavalry sprite. The red helmet, teal cloth, compact brown horse, and visible cavalry blade separate it from river archers and infantry, while the lighter armor keeps it distinct from elite Wu cavalry.
+
+## Technical Checks
+
+- base status: ok
+- action status: ok
+- base partial alpha: 0
+- action partial alpha: 0
+- base frame border hits: 0
+- action frame border hits: 0
+- base empty frames: 0
+- action empty frames: 0
+- battle scale from sample gate: 24.1..45.0 x 43.3..46.0
+- local build: passed
+- Local browser console errors: `0`
+- Local browser 404s: `0`
+
+## Notes
+
+v1 was visually readable but failed the automated height-stability gate, and v2/v3 touched action-frame borders. v4 keeps the larger base scale and slightly tightens action width so the mounted charge stays inside the 313px frame without external rings, bases, or badges.