feat(stealth): human-like click trajectories (humanize v1)

Behavioural stealth: a click that teleports the cursor to an element's exact
centre with no approach path and zero press/release delay is a tell that
advanced anti-bot vendors (Akamai/PerimeterX/DataDome) flag, even though our CDP
events are isTrusted.

New `native::humanize` module — pure, unit-tested motion maths (cubic-Bézier
eased trajectories, in-bounds landing jitter, variable keystroke cadence, and an
anti-bot vendor detector) plus a small daemon-wide runtime (current level + last
cursor + per-action seed). `dispatch_click` now moves along a curved,
decelerating path from the last cursor position and dwells before releasing.

Three levels off|fast|human. Default is Off → byte-for-byte the old teleport, so
nothing changes until opted in. `AGENT_BROWSER_HUMANIZE=human` forces it now;
the adaptive per-navigation detector (set_detected_level) and type/wheel/drag
coverage land next. 8/8 unit tests; fmt + clippy clean.

cli/src/native/mod.rs

@@ -17,6 +17,8 @@ pub mod diff;
 #[allow(dead_code)]
 pub mod element;
 #[allow(dead_code)]
+pub mod humanize;
+#[allow(dead_code)]
 pub mod inspect_server;
 #[allow(dead_code)]
 pub mod interaction;