Merge pull request 'fix(frank-archon): the state-dir guard names what the directory is now' (#39) from fix/frank-archon-state-dir-comment into main

The refusal message still named "the /data state dir"; /data left with the
prefix disk tier. The serve script mounts /models ro, the rad-tune cache and the
chat template only, and tests/frank_archon_unit.bats asserts no :/data mount
exists, so the line an operator reads at the moment a boot refuses pointed at a
mount that is gone.

Text only. The guard still refuses: the block was run standalone with the
variable unset and every neighbour set - it prints the new message and exits 1.
bash -n clean, ./tests/run.sh green (454 tests).

scripts/serve-frank-archon.sh

@@ -45,7 +45,7 @@ set +a
 : "${FRANK_ARCHON_IMAGE:?FRANK_ARCHON_IMAGE must name the radiance image}"
 : "${FRANK_ARCHON_MODEL_DIR:?FRANK_ARCHON_MODEL_DIR must name the .rad dir}"
 : "${FRANK_ARCHON_MODEL_FILE:?FRANK_ARCHON_MODEL_FILE must name the .rad file}"
-: "${FRANK_ARCHON_STATE_DIR:?FRANK_ARCHON_STATE_DIR must name the /data state dir}"
+: "${FRANK_ARCHON_STATE_DIR:?FRANK_ARCHON_STATE_DIR must name the host dir holding the rad-tune cache}"
 : "${FRANK_ARCHON_CONTAINER:?FRANK_ARCHON_CONTAINER must name the container}"
 : "${FRANK_ARCHON_SERVED_NAME:?FRANK_ARCHON_SERVED_NAME must name the alias}"
 : "${FRANK_ARCHON_PORT:?FRANK_ARCHON_PORT must be the port}"