fix(cli): close --on-change command injection via sh -c (P0) (#20)

* fix(cli): close --on-change command injection via sh -c (P0)

The --on-change flag on `webclaw watch` (single-URL, line 1588) and
`webclaw watch` multi-URL mode (line 1738) previously handed the entire
user-supplied string to `tokio::process::Command::new("sh").arg("-c").arg(cmd)`.
Any path that can influence that string — a malicious config file, an MCP
client driven by an LLM with prompt-injection exposure, an untrusted
environment variable substitution — gets arbitrary shell execution.

The command is now tokenized with `shlex::split` (POSIX-ish quoting rules)
and executed directly via `Command::new(prog).args(args)`. Metacharacters
like `;`, `&&`, `|`, `$()`, `<(...)`, env expansion, and globbing no longer
fire.

An explicit opt-in escape hatch is available for users who genuinely need
a shell pipeline: `WEBCLAW_ALLOW_SHELL=1` preserves the old `sh -c` path
and logs a warning on every invocation so it can't slip in silently.

Both call sites now route through a shared `spawn_on_change()` helper.

Adds `shlex = "1"` to webclaw-cli dependencies.

Version: 0.3.13 -> 0.3.14
CHANGELOG updated.

Surfaced by the 2026-04-16 workspace audit.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* chore(brand): fix clippy 1.95 unnecessary_sort_by errors

Pre-existing sort_by calls in brand.rs became hard errors under clippy
1.95. Switch to sort_by_key with std::cmp::Reverse. Pure refactor — same
ordering, no behavior change. Bundled here so CI goes green on the P0
command-injection fix.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

crates/webclaw-cli/Cargo.toml

@@ -24,3 +24,4 @@ tracing-subscriber = { workspace = true }
 reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls"] }
 regex = "1"
 url = "2"
+shlex = "1"