fix(runtime): road-gated diagnostics fire unconditionally and cite closed sprints in user-visible text

[JArmandoAnaya]

What

User-visible diagnostics still describe the pre-road-backend world and cite closed internal sprints/issues. Worst class: the four init-time condition warnings fire unconditionally — validate_condition_expression (core/src/engine.cpp:388-394) has no road-query parameter — so a scenario running on a real OpenDRIVE map is told its working condition is "a deterministic false until p3-s4":

• core/src/engine.cpp:329-331 (road-based distance modes), :667-669 (EndOfRoad), :676-678 (Offroad), :702-704 (RelativeClearance) — all say "deterministic false until p3-s4", yet road_integration_test.cpp:382,410 proves EndOfRoad/Offroad evaluate with a backend attached
• core/src/engine.cpp:3654-3656 — lane-change diagnostic cites closed issue "[p3-s4] Road-based positions in actions & conditions #23"
• capi/include/scena/capi.h:254-256 — public header claims road-based systems "are not implemented yet"; they degrade only when no IRoadQuery is attached (engine.cpp:3421,3806)
• frontends/xml/src/loader.cpp:426-427 — standalone Catalog documents warn "not loaded yet (p4-s4)"; p4-s4 landed catalog loading via CatalogLocations. Either support standalone catalog documents or reword and record the actual scope; the pinning test (xml_infra_test.cpp:484-493) never asserts the message
• Stale comments blaming closed sprints: engine.cpp:484, runtime/scheduler.cpp:794 (p5-s4), engine.cpp:1561, ir/bounding_box.h:25-44 (p2-s1), frontends/dsl/src/lower.cpp:461,579,973 ([p8-s2] Composition operators: serial, parallel, one_of #45/[p8-s3] Movement modifiers #46), lower.cpp:941 ("a later sprint")

Done when

• The four init warnings are emitted only when no road network is attached, and their text states that condition ("no road network attached"), not a sprint id
• No user-visible diagnostic or public header cites an internal sprint id or issue number
• Messages pinned in tests so wording regressions are caught
• Stale closed-sprint code comments swept (grep for p[0-9]-s[0-9] and #[0-9]+ outside docs/roadmap)