release(ways): bump to 1.7.3

[aaronsb]

Version bump for 1.7.3.

Contains #430 — firing-window and session-detection fixes:

• The way-firing curve is no longer latched at first fire. EngagementState serializes its curve, and load_engagement was discarding the freshly-resolved one, so a way whose first fire landed before the transcript named a model kept half_life = refire x 200_000 for the whole session (closes Firing window latched at first fire: persisted curve + defaulted window on launch race #426).
• The firing window resolves from the firing session, with both candidates filtered on window_source so a defaulted 200k never shadows a real detection.
• ways list auto-detect requires a resolvable transcript and distinguishes "no markers" from "markers, no transcript" (closes ways list auto-detect accepts sessions with no transcript #427).

Follow-ups tracked in #428 and #429.