feat(ui): Streamlit polish — joint H+V, PPHPD, console, GeoJSON import

[harsh-pandhe]

Summary

Brings the optimizer UI up to the operator-facing feature set the Phase 2 MVP lacked, following the requested UI blueprint (sidebar inputs · viewport tabs · bottom console).

• Joint H+V control — a "Corridor half-width" sidebar slider wires Phase 12c into the UI. Above 0 (GA mode) the run builds a surface_fn from the DEM swath and passes it to optimize(), so the GA may shift towers laterally to route around terrain; the console reports how many towers ended up offset. NSGA-II mode shows an info note (GA-only feature).
• PPHPD capacity metric — a line-speed slider plus a "Capacity" headline metric: persons per hour per direction, derived from cabin spacing and line speed.
• Bottom run console — a persistent expander logging each run: terrain extent, optimizer config, feasibility, and violation detail.
• GeoJSON import — upload a previously-exported alignment.geojson in the Projects tab; the tower schedule is parsed, displayed, and re-evaluated against the current terrain run (feasible / violations).

Test plan

• python -m py_compile app/streamlit_app.py — syntax clean
• App boots headless (streamlit run --server.headless true) and serves / without exception
• Pure helpers (_pphpd, _log) exercised in isolation
• UI-only change — app/streamlit_app.py + CHANGELOG; no effect on the optimizer/test suite (157/157 unchanged)

Note: this UI is not covered by the automated suite; the run-path logic delegates to optimize(surface_fn=…) which is covered by tests/test_joint_hv.py.

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