feat(hardware): JLCPCB assembly files for 48V

Context: the 48 V sub-board gerbers exist; assembly at JLCPCB needs
BOM and CPL with sourced LCSC references. The repo-wide *.csv ignore
rule silently excluded them, hence a scoped exception.

Approach: CPL exported from the routed PCB (kicad-cli pos, JLCPCB
column format); BOM consolidated with LCSC parts verified in stock.

Changes:
- .gitignore: allow **/jlcpcb/assembly/*.csv
- Add jlcpcb/assembly/BMU_switch_mosfet_48v_bom.csv: IRF5210 C2622,
  MMBTA42 C8515 (CJ), BZT52C12 C43491 (CJ), 10K 0603 C25804 (basic),
  15K 0402 C25756 (basic), header C32713268, IDC 2x5 C7501191
- Add jlcpcb/assembly/BMU_switch_mosfet_48v_cpl.csv: 21 placements
  (U1 excluded from position files by design - hand-soldered THT)

Impact: the 48 V sub-board can be ordered assembled; SOT-23/D2PAK
rotations may need the usual one-time check in the JLCPCB viewer.

.gitignore

@@ -62,6 +62,8 @@ _autosave-*
 *.csv
 # Exception: PlatformIO partition tables
 !partitions*.csv
+# Exception: fichiers d'assemblage JLCPCB versionnés
+!**/jlcpcb/assembly/*.csv
 
 ### KiCad Patch ###
 rescue-backup/

hardware/pcb-bmu-v2/BMU_switch_mosfet_48v/jlcpcb/assembly/BMU_switch_mosfet_48v_bom.csv

@@ -0,0 +1,8 @@
+Comment,Designator,Footprint,LCSC Part #
+IRF5210STRLPBF (P-MOSFET 100V),"Q2,Q3,Q4,Q5,Q7,Q8,Q9,Q10",TO-263-2 (D2PAK),C2622
+MMBTA42 (NPN 300V),"Q1,Q11",SOT-23,C8515
+BZT52C12 (zener 12V),"D1,D2",SOD-123,C43491
+10K 1%,"R1,R2,R3,R4,R5",R0603,C25804
+15K 1%,"R6,R7",R0402,C25756
+HX PZ2.54-1X2P (header 2P),U1,P2.54 1x2 THT,C32713268
+ZX-IDC2.54-2-5PZZ (IDC 2x5),"U2,U3",IDC 2x5 THT,C7501191

hardware/pcb-bmu-v2/BMU_switch_mosfet_48v/jlcpcb/assembly/BMU_switch_mosfet_48v_cpl.csv

@@ -0,0 +1,22 @@
+Designator,Mid X,Mid Y,Layer,Rotation
+U2,139.0129mm,-140.0749mm,Bottom,90.0
+U3,135.6300mm,-122.8012mm,Bottom,180.0
+D1,160.0000mm,-128.8000mm,Top,90.0
+D2,128.8000mm,-127.8600mm,Top,-90.0
+Q1,160.2000mm,-146.9000mm,Top,180.0
+Q2,153.5000mm,-110.7412mm,Top,180.0
+Q3,153.5000mm,-96.2500mm,Top,180.0
+Q4,153.5000mm,-85.1012mm,Top,180.0
+Q5,153.5000mm,-71.5312mm,Top,180.0
+Q7,134.9200mm,-71.5312mm,Top,0.0
+Q8,134.9200mm,-85.1012mm,Top,0.0
+Q9,134.9200mm,-96.2500mm,Top,0.0
+Q10,134.9200mm,-110.7412mm,Top,0.0
+Q11,154.3500mm,-148.2400mm,Top,90.0
+R1,157.0000mm,-148.2812mm,Top,90.0
+R2,160.7500mm,-132.0000mm,Top,180.0
+R3,159.5000mm,-141.7812mm,Top,0.0
+R4,159.5000mm,-143.7812mm,Top,0.0
+R5,126.2000mm,-127.8563mm,Top,90.0
+R6,161.9000mm,-138.5000mm,Top,90.0
+R7,126.0300mm,-131.5000mm,Top,90.0