feat(bus): the bus host runs an explicit Claude Code binary (#1561, row 68)

MOSAIC_CLAUDE_BIN names the claude binary by absolute path instead of
finding it on PATH. scripts/bus-service.sh render|install --claude PATH
writes it into the unit (default: command -v claude in the installing
shell); the claude adapter, the launcher's version read and the seat
session environment all use it. Mos's Q18 ask: the unit's PATH found
/usr/bin/claude 2.1.259, which refuses claude-opus-5-5.

Candidate: round 2 manifest 21c1ab05, round 1 (a2008d8b) rebased onto
f2f2861b after row 55 changed docs/TOOLS.md and packages/cli/README.md;
the changed lines are byte-identical. Approved by Filbert (27349, 27374)
and Dewey (27350, 27375). Sage's gate on f2f2861b plus the patch: cli
112, seat 27, harness 57, nine scripts/test-*.sh 0 failed, Docker on.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/cli/systemd/mosaic-bus.service.in

@@ -1,6 +1,6 @@
 # Mosaic bus host, one instance per business: mosaic-bus@<business>.
-# Rendered by scripts/bus-service.sh from packages/cli/systemd/; @REPO@ and
-# @PATH@ are filled in at install time. Edit the template and reinstall; do
+# Rendered by scripts/bus-service.sh from packages/cli/systemd/; @REPO@,
+# @PATH@ and the claude line below are filled in at install time. Edit the template and reinstall; do
 # not edit the installed copy. The bus store allows one broker per data
 # root, so run one instance per data root (packages/cli/README.md).
 [Unit]
@@ -13,6 +13,10 @@ StartLimitBurst=5
 Type=simple
 WorkingDirectory=@REPO@
 Environment=PATH=@PATH@
+# The Claude Code binary that managed sessions and the manifest's
+# claudeVersion run, pinned at install (`--claude PATH`, default
+# `command -v claude`). Without it they run `claude` from PATH above.
+@CLAUDE_ENV@
 # The host reads the system config and the business file, boots the broker
 # (packages/bus/src/process.mjs) and starts the notifier. Config problems and
 # refusals exit 3, usage 4, invalid input 2: none of those is retried. A