refact(deployer): one MainPID gate for all three LLM endpoints

frank-dragoon's health gate never checked WHO answered :7770 — the
false-green the fleet learned about on 2026-09-26 (a stray probe holding
the port satisfies a bare curl while the unit is stopped). The other two
handlers carried that check as inlined copies; all three now call
assert_unit_owns_port, and dragoon gets the protection it was missing.

The seam follows: the endpoints' text-grep deployer tests are deleted,
because tests/llm_deploy_gates.bats EXECUTES the same handlers end to end
(stub systemctl/podman/sudo/ss/curl) and asserts refusals, restarts, unit
links, the pending marker, and the MainPID hardening. GATE_PREFIX is
exported at each handler for the same reason the serve scripts export it.

tests/llm_deploy_gates.bats

@@ -23,11 +23,14 @@ teardown() { sandbox_teardown; }
     [ "$(restarts_requested)" = "0" ]
 }
 
-@test "the dragoon handler refuses a truncated checkpoint, naming both sizes" {
+@test "the dragoon handler refuses a truncated checkpoint, pointing at the fetch" {
     truncate -s 9 "$STAGE/models/ck.hgn"
     run_handler dankclaw frank-dragoon
     [ "$status" -ne 0 ]
     [[ "$output" == *"checkpoint: is 9 bytes, expected 10"* ]]
+    # The refusal is only useful if it names the remedy: the fetch script
+    # re-verifies byte counts and hashes.
+    [[ "$output" == *"download-frank-dragoon-flashnext.sh"* ]]
     [ "$(restarts_requested)" = "0" ]
 }