CMake: Fix stale staging of headers, modules list, and temporal SQL in build output

[petrasovaa]

These were identified problems by AI during unrelated work, below is the AI explanation. Probably not high priority, but could be useful.

This PR fixes three CMake staging defects that leave the runnable tree under build/output stale or incomplete, typically after editing headers or switching branches. Each showed up as confusing failures unrelated to
the change under test.

What changed:

• Staged headers now refresh. The copy command in include/CMakeLists.txt had no DEPENDS, so once a header was staged it was never re-copied. Editing a header (e.g. include/grass/gis.h) caused compilation against the stale copy and GIS_H_VERSION mismatch fatal errors at runtime.

• Stale modules no longer linger in ALL_MODULES. Modules append themselves to modules_list as CACHE INTERNAL, but the top-level set(modules_list) only cleared the normal variable, so the cached list accumulated across configures. After switching to a branch where a module no longer exists, builds failed with "No rule to make target". The cache entry is now reset at the start of each configure, before any module registers, which keeps the previous membership (including the helper programs from lib/ and utils/) while dropping stale entries.

• Temporal SQL templates are staged. lib/temporal/SQL/*.sql were install-only, so temporal database creation failed when running from build/output before cmake --install. They are now copied next to the library, following the lib/gis etc-file staging pattern. As with that pattern, the copy runs when the library relinks, not when only a .sql file changes.

Verification:

• Touching gis.h and building INCLUDE_HEADERS re-runs the copy.
• A bogus module name injected into the cached modules_list disappears on reconfigure, and the pre-existing helper program entries are kept.
• After deleting the staged etc/sql, rebuilding grass_temporal stages all 30 .sql files (and only those, not the Makefile in the same directory).

AI disclosure: implemented and verified by Claude (Fable).

[nilason]

Thanks, in particular the header files have bothered me for a while, but I always kicked that can further down the road.