TSSIM/JESIM final v47 - finite-fault stamp automatic subsidence

Base: v46 Mercator scale fix.

New behavior:
- Finite-fault stamp mode now regenerates a down-dip subsidence lobe automatically.
- Press N or Enter to complete the current stamp fault; the source field is rebuilt with generated subsidence.
- Press G while in stamp mode to manually regenerate the automatic subsidence from existing stamped rupture nodes.
- Loading a preset also regenerates automatic subsidence, so v46 presets saved with only stamped uplift/footprint nodes will still get the negative lobe.

Implementation notes:
- Positive uplift / footprint source nodes keep fault_id > 0 and patch_id > 0.
- Generated subsidence nodes use the same positive fault_id but negative patch_id, slip_m=0, and height_m<0.
- Regeneration first removes old generated subsidence nodes, then rebuilds them, so repeated loading/saving does not duplicate the lobe.
- M0/Mw still counts only direct rupture footprint nodes; generated subsidence remains excluded from moment area.
- Land-side generated subsidence is skipped.

Unchanged from v46:
- Calibrated Mercator km/cell scale.
- First stamp defines the fault plane; down-dip stamp rows get deeper.
- Nearest-stamp bridging.
- Ctrl+Z source undo.
- Advanced node tuning / multiselect / box select.
- JESIM 5-minute observations and packet_meaningful_update.
- 清水 removed from observation table.
- Transmit-only 60-hour cap.
- External wall-clock 1x observation timing.
- No y-axis flip.
