fix(env): one login-shell-derived PATH for every spawned tool (T-439)

Desktop/dock-launched clide inherits a sparse PATH (no ~/.local/bin, brew,
nvm, …), so pql/git/claude and PTY tools went missing. T-347 fixed only the
toolchain/pql path on Linux; env.dart's expander was still macOS-only and
claude/PTY/git used the raw PATH — the breakage recurred per spawn site
because there were three divergent expanders.

Consolidate into one resolver (lib/src/env/shell_env.dart):
- primeLoginShellPath(): probe the user's real login shell once at startup
  (`$SHELL -l -c`, sentinel-framed, bounded timeout, graceful fallback to the
  process PATH). Captures the user's actual PATH, not a hardcoded guess.
- expandToolPath(): the canonical merge (moved from toolchain_paths, which
  re-exports it for its tests) — unions the well-known user/local bin dirs.
- resolvedToolPath(): currentSearchPath() + expandToolPath, the single call
  every spawn site uses.

Routed through it: PTY children (registry.dart now overrides PATH), git
(env.dart → operations.dart), the toolchain probe (toolchain_paths), and
hosted claude (agent_bootstrap). Primed in main.dart's !kIsWeb boot. Deleted
the macOS-only env.dart copy and the cli_install copy.

Tests: new shell_env_test (probe + every fallback + merge); env_test and
cli_install_test updated to the consolidated surface. analyze clean, web wasm
build still green, make test green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/builtin/claude/src/agent_bootstrap.dart

@@ -23,6 +23,7 @@ library;
 
 import 'dart:io';
 
+import 'package:clide/src/env/shell_env.dart' show resolvedToolPath;
 import 'package:clide/src/ipc/paths.dart' show workspaceSocketPath;
 
 // Web fence (T-438, D-100): `Abi.current()` (dart:ffi) is desktop-only; the web
@@ -108,7 +109,10 @@ class AgentBootstrap {
 /// orchestrator merges both into one `--append-system-prompt`.
 AgentBootstrap agentBootstrap(String workspaceRoot, {Map<String, String>? base}) {
   final home = Platform.environment['HOME'];
-  final currentPath = (base ?? Platform.environment)['PATH'] ?? Platform.environment['PATH'];
+  // The login-shell-resolved PATH (T-439) so a hosted claude — and the tools it
+  // shells out to — find user-installed components on a desktop launch, not just
+  // the sparse GUI PATH. agentEnvDelta still prepends the clide-CLI dir.
+  final currentPath = resolvedToolPath();
   final candidates = <String>[
     if (home != null && home.isNotEmpty) '$home/.local/bin',
     '$workspaceRoot/native/${currentNativeDirName()}',