Promote NES PowerPad Test Card (U) from _wip to top-level project

Moves NES PowerPad Test Card (U) from _wip/ to NES PowerPad Test Card (U)/ with full ROM build:
- Adds header.s, chr.s, linker.cfg (HEADER+PRG+CHR segments)
- Updates Makefile to build and verify reconstructed.nes vs rom.nes
- Adds rom.nes copy + copilot/rom.nes symlink per repo convention
- Verified byte-identical build

Pass 1 complete: full code/data classification (~7.2% code / ~92.8% data)
Pass 2 complete: routine headers for all ~50 labels, semantic naming for key
routines (Reset, NmiHandler, VramWrite, ReadPad, ProcessPads, etc.),
zero-page aliases in locals.inc (Zp00-Zp15)
Pass 3 complete: data tables named (PaletteData at ,
PadBitTableLives at )

Root OVERVIEW.md updated:
- Removes NES PowerPad Test Card from _wip skeleton table (21 → 20 skeletons)
- Adds NES PowerPad Test Card as #15 in numbered inventory (BYTE-IDENTICAL, Pass 2/3)
- Updates summary count from 14 to 15 projects

NES PowerPad Test Card (U)/copilot/linker.cfg

@@ -0,0 +1,10 @@
+MEMORY {
+  HEADER: start = $0000, size = $0010, fill = yes;
+  PRG:    start = $C000, size = $4000, file = %O, fill = yes;
+  CHR:    start = $0000, size = $2000, file = %O, fill = yes;
+}
+SEGMENTS {
+  HEADER: load = HEADER, type = ro;
+  PRG:    load = PRG,    type = ro;
+  CHR:    load = CHR,    type = ro;
+}