Move a module on a merge only when its build source holds a changed file (hq ADR 0267, issue 363)

Every merge to the controller's repository planned the controller, the
build seat's holder and the route proxy in three gated tiers, whatever it
changed (issue 338). The planner now maps a merge's files onto the build
source each module's newest trunk build said: a README moves nothing, the
controller's command the controller alone, the proxy's program the proxy
alone. A module with none said, or one an open plan has yet to build, is
read whole as before. Sharing a repository draws no packages edge any more,
and one recorded before neither widens nor orders a plan.

internal/inventory/migrations/0088-a-build-says-its-build-source.sql

@@ -0,0 +1,9 @@
+-- A build says what it was made from, as files (novox/hq ADR 0267, issue 363).
+--
+-- A merge to a repository moved every module whose build read it, whatever the files: the controller,
+-- built from its repository's root, and the two images whose context is that repository (issue 338).
+-- A build of a trunk commit now says its build source per repository — a Go program's import closure,
+-- an archive's directory, an image's recipe — and the planner maps the next merge's changed files onto
+-- the build source of the module's newest build. Null for a build that said none (one off the trunk,
+-- one from a builder that predates this, one whose source is not known): its module is read as before.
+alter table build add column build_sources jsonb;