launcher: log session/IME env block at startup (#570)

* launcher: log session/IME env block at startup (#548)

Adds log_session_env, called once per launch from each packaging
target (deb, rpm, AppImage, Nix). Emits a single env={ ... } block
covering display (XDG_SESSION_TYPE, WAYLAND_DISPLAY, DISPLAY,
XDG_CURRENT_DESKTOP), IME (GTK_IM_MODULE, XMODIFIERS, QT_IM_MODULE),
and Claude-specific overrides (CLAUDE_USE_WAYLAND,
CLAUDE_TITLEBAR_STYLE, CLAUDE_GTK_IM_MODULE).

Empty/unset values are emitted as `KEY=` (rather than omitted) so
absence is unambiguous in bug reports. Pure observability — no
behavior change.

Closes #548

Co-Authored-By: Claude <claude@anthropic.com>

* test: consolidate log_session_env BATS coverage (#548)

Collapse the four log_session_env cases into two, and tighten the
assertions in both:

  - Old test 1 (substring match per key) + old test 4 (block braces
    on their own lines) → one test using exact-line equality on the
    `lines` array. Locks block structure and per-key formatting in
    a single pass; substring matching could not catch a regression
    that re-ordered keys, dropped indentation, or merged lines.
  - Old test 2 (unset values are KEY=) + old test 3 (empty-string
    is KEY=) → one test covering both code paths. Exact-line match
    proves the value after `=` is truly empty; the previous
    `*'KEY='*` substring would have matched `KEY=value` and the
    old test-3 regex was fragile (depended on trailing newline
    being literal `$'\n'` vs end-of-string `$`).

Net: 77 → 42 lines, 4 → 2 cases, stronger guarantees. No change to
the helper itself or the call sites — issue #548 acceptance criteria
still hold.

---------

Co-authored-by: Claude <claude@anthropic.com>

nix/claude-desktop.nix

@@ -245,6 +245,7 @@ cleanup_stale_cowork_socket
 log_message '--- Claude Desktop Launcher Start (NixOS) ---'
 log_message "Timestamp: $(date)"
 log_message "Arguments: $@"
+log_session_env
 
 # Check for display
 if ! check_display; then