feat: typed settings fields, timeline zoom, faster dev builds

Footage budget, clip hotkey length and bookmark before/after are now typed
fields (m:ss or seconds), validated on Enter or blur and reverted when out of
range. Scrolling over the session timeline zooms around the pointer (down to
10 s) and scrolling sideways or with Shift pans, with a Fit button.

Settings felt slow because GPUI ran unoptimised: dev builds now optimise
dependencies, taking first frames from 200-300 ms to about 15 ms. Adds
rig-pointer, a virtual pointer for driving the interface in the headless
rig, which verified the fields, zoom and timeline dragging.

Cargo.toml

@@ -4,6 +4,7 @@ members = [
     "crates/clipbin-desktop",
     "crates/clipbin-obs",
     "crates/clipbin-probe",
+    "crates/rig-pointer",
 ]
 default-members = ["crates/clipbin-desktop"]
 resolver = "3"
@@ -30,6 +31,11 @@ unsafe_code = "forbid"
 [profile.dev]
 debug = 1
 
+# GPUI is far too slow to use unoptimised; optimise dependencies even in dev
+# builds (our own crates stay quick to rebuild).
+[profile.dev.package."*"]
+opt-level = 2
+
 [profile.release]
 lto = "thin"
 codegen-units = 1