Allow travel across visibly harmless traps - #1689

Automatic travel refuses routes across known traps that cannot affect you when flying or levitating.

Use the existing clear-immunity check when planning travel and deciding whether a known trap should stop it. Both flying and levitation allow routing across harmless floor-triggered traps, including fire traps and land mines. Preserve the travel route and suppress per-trap messages when flying or levitating over those traps.

Discovering a trap, secret door, or hidden passage still interrupts travel. An unnoticed airborne flyover does not discover a trap. Existing water and lava routing rules are unchanged, including the deliberate restriction on starting lava-walking travel from land.

Ordinary running still stops at known traps. Hallucination still prevents trusting a known trap's identity. Sokoban pits and holes remain blocked, and forced trap activation retains its normal behavior. Travel does not infer safety from non-obvious resistances. The change is recorded in doc/fixes5-0-1.txt.

Validation: the trap-routing portion packages the existing local travel changes. Re-ran the three travel test suites in both existing terminal and Qt test executables; all six passed. Coverage includes routing and stopping decisions, flying and levitation over all 14 floor-triggered trap types, known and unknown airborne flyovers preserving travel without messages, mounted routing, grounded and forced fire traps stopping travel, hallucination, ordinary running, and Sokoban restrictions. These are game-engine tests using wizard fixtures, including Qt builds running with the terminal interface; they are not Qt UI tests. git diff --check passes.