feat(dsl): movement actions, the map file and scena-run .osc (p8-s1)

[JArmandoAnaya]

Completes p8-s1: a DSL scenario now runs end to end.

scena-run cruise.osc --dt 0.01 --duration 12 --trace out/cruise.csv

§8.8 movement actions → IR actions

Seven have an unambiguous counterpart and lower; the runtime is the one both
frontends already share, so lowering decides only which IR action a DSL action
is.

§8.8 action	IR action
assign_speed	SpeedAction, Step
change_speed	SpeedAction with the transition §8.8.2.18 asks for
remain_stationary	SpeedAction to zero
assign_position	TeleportAction to a WorldPosition
change_lane	LaneChangeAction with a RelativeTargetLane
change_space_gap / change_time_gap	LongitudinalDistanceAction

move, drive and walk carry no target of their own — they exist to be
shaped by §8.9 modifiers (p8-s3) — so on their own they lower to nothing.
Everything else in §8.8 is reported by name, never silently dropped.

Two readings the standard does not state, both recorded in ADR-0030:

• dynamic_profile names a shape, rate_peak a magnitude, and neither is a
  duration. With no peak rate there is no number to ramp over, so the change
  is a Step (§7.4.1.2). asap is a Step from the other direction: §8.7
  declares no performance envelope, so "as soon as possible" is bounded by
  nothing.
• change_lane needs an explicit left or right. §8.8.3.14's inside,
  outside and same need road geometry to say which way that is, and an
  unstated side would have to be chosen — which the determinism contract
  does not allow.

The do directive → a storyboard

One Story, one Act, one ManeuverGroup per phase — the group is where an actor
lives, so a group per phase keeps each invocation's actor with its actions.
serial chains a phase on its predecessor reaching completeState, which is the
trigger form §7.6.2.1.2's "starts when its predecessor ends" already has in the
runtime; parallel leaves the triggers absent (§7.6.1.1). one_of, nesting,
until, wait, emit, call and an invocation duration are reported and
belong to p8-s2.

The map file, and one resolution rule it needed

§8.5.4's map_file is read in both spellings the standard prints —
map.set_map_file("m.xodr") (Code 61) and keep(my_map.map_file == "m.xodr")
(Code 62) — and travels beside the IR in a LowerResult, mirroring
xml::Document. A road-network path is an input to the host, not kernel
state: the engine reaches roads only through IRoadQuery (ADR-0003).

The first spelling needed something the checker did not have: a bare actor
type name is a receiver in its own right. map in Code 61 names the actor
type, because the road network is a singleton no scenario declares a field
for, and without that rule the standard's own concrete-scenario example
(Code 6) was rejected. A declared field of the same name still wins — the
receiver a reader means by a name is the declaration in front of them.

Struct-valued arguments

The DSL has no struct constructor: §7.2.2.6.7 declares list and range
constructors and nothing else. So assign_position(position: start) can only
name a declaration, and the keeps on it are where the numbers are — the same
binding table ADR-0030 already uses for an actor's own attributes, applied one
level further out. A coordinate nothing constrains is reported, not assumed.

scena-run runs .osc

The extension picks the frontend; everything past the load sees only the
Scenario IR, so the options, exit codes and trace format are unchanged.
--entry names the §7.7.2 entry point (a file with several scenarios is
reported, never guessed at) and -I adds an import search path.

Tests and docs

• dsl_lowering_test.cpp 17 → 37: each action's mapping, the storyboard shape,
  both map-file spellings, and every deferral reported rather than dropped.
• dsl_types_test.cpp +3: the actor-type receiver, a field shadowing it, and a
  non-actor type still getting the ordinary "that is a type, not a value".
• scena_run_test.cpp +4: a .osc running end to end, --entry selection, a
  malformed .osc, and the DSL-named road network.
• ADR-0030 gains decisions 6–8 and two rejected alternatives; the coverage
  matrix, the scena-run user guide and the DSL frontend README move with the
  code.
• The parity audit now reads lower.h as well, so dsl::lower's missing
  binding is recorded with its reason instead of being invisible — the IR has
  no binding carrier until p8-s4 ([p8-s4] XML-DSL parity & DSL golden scenarios #47).

1366 gtest (+27), 194 pytest.

Closes #44