Import claude-code-switcher from the Windows build

Source of truth so far has been c:\Users\smoido\projects\cli on the Windows
box, which has no git history of its own. This is that tree copied verbatim over
SSH, minus dist/ - the PowerShell build, the POSIX port under linux/, and the
presets both share.

Recorded as its own commit so that everything after it is a reviewable diff
rather than an undifferentiated first drop.

linux/shell-snippet.sh

@@ -0,0 +1,40 @@
+# >>> claude-mode >>>
+# Installed by claude-code-switcher. Do not edit between the markers;
+# re-run install.sh instead.
+#
+# `claude-mode` itself is a normal executable on PATH, so nothing here is needed
+# to use it. This block exists only for the wrapper below.
+#
+# settings.json is the single source of truth for gateway config, so any
+# inherited copy of these variables is stripped before launch: a stale
+# ANTHROPIC_API_KEY would silently bypass the gateway, and stale
+# ANTHROPIC_BASE_URL / *_MODEL values would break native Anthropic auth. Only
+# the child process is affected - the rest of your shell is untouched.
+claude() {
+    local real
+    real="$(command -v claude 2>/dev/null)"
+    if [ -z "$real" ] || [ "$real" = "claude" ]; then
+        # `command -v` resolved to this function; find the real binary on PATH.
+        real="$(type -P claude 2>/dev/null)"
+    fi
+    if [ -z "$real" ]; then
+        echo "claude: not found on PATH" >&2
+        return 127
+    fi
+    env -u ANTHROPIC_API_KEY \
+        -u ANTHROPIC_AUTH_TOKEN \
+        -u ANTHROPIC_BASE_URL \
+        -u ANTHROPIC_DEFAULT_OPUS_MODEL \
+        -u ANTHROPIC_DEFAULT_SONNET_MODEL \
+        -u ANTHROPIC_DEFAULT_HAIKU_MODEL \
+        -u ANTHROPIC_DEFAULT_FABLE_MODEL \
+        -u CLAUDE_CODE_SUBAGENT_MODEL \
+        -u CLAUDE_CODE_ENABLE_GATEWAY_MODEL_DISCOVERY \
+        -u CLAUDE_CODE_ATTRIBUTION_HEADER \
+        -u CLAUDE_CODE_AUTO_COMPACT_WINDOW \
+        -u CLAUDE_CODE_MAX_CONTEXT_TOKENS \
+        -u CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC \
+        -u API_TIMEOUT_MS \
+        "$real" "$@"
+}
+# <<< claude-mode <<<