Refresh data: fix gx prefix mapping (Gaia-X)

[kevinschaper]

Regenerates the prefix contexts via `make etl` to pull in current upstream data.

Highlights

• `gx` → `https://w3id.org/gaia-x/development#\` in all merged contexts and `prefixcc.csv`. The dead Graphite/Synaptica mapping was outvoted at prefix.cc, so the refresh picks up the correct Gaia-X namespace automatically (no curated override needed). Fixes gx prefix maps to dead Graphite/Synaptica namespace instead of Gaia-X #82.
• Other churn is routine upstream refresh: w3id (+298 prefixes), prefix.cc drift (+93/-29), two new OBO prefixes (PBPKO, PREFER), and GO xref namespace modernizations.

Notes

• `gax` → `http://w3id.org/gaia-x/core#\` remains, as it is still present (and not yet removed) at prefix.cc; it cannot be removed from a local curated source.

Verification

• `make test` → 27 tests, OK (1 skipped).

After merge, this unblocks cutting the requested v0.2.8 release.