feat(ble): replace blocking scan with advertisement observation

The one-shot scan kept only the top six devices by RSSI and dropped the
advertisement payload, so a distant beacon lost its slot to nearby phones
and its data was unreachable -- wrong on every axis for reading sensors
that broadcast in their adverts.

Replace it with a continuous observer: observe(filter)/observed()/
unobserve()/isObserving(). BleObservation carries the raw advertisement
bytes for Lua to parse, and BleFilter keeps only adverts matching a
service-data UUID or manufacturer id.

lua/api/core/ble.lua

@@ -2,10 +2,16 @@
 
 -- Generated from native/src/bindings/core/ble.cpp. Do not edit.
 
----@class BleDevice
----@field name string
+---@class BleObservation
 ---@field address string
+---@field name string
 ---@field rssi integer
+---@field payload string Raw advertisement bytes.
+---@field lastSeenMs integer sys.getMillis() at last sighting.
+
+---@class BleFilter
+---@field services? string[] Service-data UUIDs to keep.
+---@field manufacturers? integer[] Manufacturer ids to keep.
 
 ---@class BleLib
 ble = {}
@@ -23,11 +29,22 @@ function ble.deinit() end
 ---@return boolean
 function ble.isInitialized() end
 
----Scans for advertising devices.
----@param durationMs? integer Defaults to 3000.
----@return BleDevice[]? devices
+---Starts passively observing advertisements, coalesced per device.
+---@param filter? BleFilter Keep only matching adverts; nil keeps all.
+---@return true? ok
 ---@return string? error
-function ble.scan(durationMs) end
+function ble.observe(filter) end
+
+---Stops observing and clears the snapshot.
+function ble.unobserve() end
+
+---Whether advertisement observation is running.
+---@return boolean
+function ble.isObserving() end
+
+---The current snapshot of observed devices.
+---@return BleObservation[] devices
+function ble.observed() end
 
 ---Connects to a peripheral.
 ---@param address string