remove the Shift copy-building-settings gesture

REQ-BLD-COPY-CONFIG is dropped: Shift+right-click no longer caches a
building's recipe / schematic+layout / splitter filters, Shift+left-click
no longer stamps them onto same-type buildings, and the cyan eligible-
target tint and copy/paste flashes go with them. Shift+left-click now
falls through to normal selection, which needs no code of its own -- only
Ctrl is meaningful to selection (REQ-UI-MULTI-SELECT), so dropping the
branch that consumed the click is enough.

readBuildingConfig stays. It had two callers, and the other one is
captureBlueprintFromSelection, which needs it to record each blueprint
building's configuration (REQ-UI-BLUEPRINT-STORAGE). Its five tests stay
too, retagged [blueprint] and rewritten to name the caller that is left.

The visuals.toml copy_config colour is removed together with its
VisualsConfig field and its loader line: overlay keys are mandatory, so
those three have to move as one or startup aborts.

REQ-BLD-COPY-CONFIG-FEEDBACK, cited by four of these files and by the TOML
comment, never existed in requirements.md; deleting the citations retires
a dangling id.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JcReq7hVk4KUPhTDKWAG7K

src/lib/sim/BuildingConfig.h

@@ -15,8 +15,8 @@ struct BuildingsConfig;
 
 // The user-configurable settings of a single building or construction site: the
 // selected recipe / ship schematic, the shipyard module layout, and (for
-// splitters) the two output filters. Shared by the copy-settings gesture
-// (REQ-BLD-COPY-CONFIG) and blueprint capture (REQ-UI-BLUEPRINT-STORAGE).
+// splitters) the two output filters. This is what blueprint capture records per
+// constituent building (REQ-UI-BLUEPRINT-STORAGE).
 struct BuildingConfig
 {
     BuildingType type = BuildingType::Miner;