feat(display.go): Add display brightness settings (#17)

* feat(display.go): impl setDisplayBrightness()

Implements setDisplayBrightness(brightness int) which allows setting the
backlight brightness on JetKVM's hardware.

Needs to be implemented into the RPC, config and frontend.

* feat(config): add backlight control settings

* feat(display): add automatic dimming & switch off to display

WIP, dims the display to 50% of the BacklightMaxBrightness after
BacklightDimAfterMS expires. Turns the display off after
BacklightOffAfterMS

* feat(rpc): add methods to get and set BacklightSettings

* WIP: feat(settings): add Max backlight setting

* chore: use constant for backlight control file

* fix: only attempt to wake the display if it's off

* feat(display): wake on touch

* fix: re-use buffer between reads

* fix: wakeDisplay() on start to fix warm start issue

If the application had turned off the display before exiting, it
wouldn't be brought on when the application restarted without a device
reboot.

* chore: various comment & string updates

* fix: newline on set brightness log

Noticed by @eric
https://github.com/jetkvm/kvm/pull/17#discussion_r1903338705

* fix: set default value for display

Set the DisplayMaxBrightness to the default brightness used
out-of-the-box by JetKVM. Also sets the dim/timeout to 2 minutes and 30
mintes respectively.

* feat(display.go): use tickers to countdown to dim/off

As suggested by tutman in https://github.com/jetkvm/kvm/pull/17, use
tickers set to the duration of dim/off to avoid a loop running every
second. The tickers are reset to the dim/off times whenever
wakeDisplay() is called.

* chore: update config

Changed Dim & Off values to seconds instead of milliseconds, there's no
need for it to be that precise.

* feat(display.go): wakeDisplay() force

Adds the force boolean to wakedisplay() which allows skipping the
backlightState == 0 check, this means you can force a ticker reset, even
if the display is currently in the "full bright" state

* feat(display.go): move tickers into their own method

This allows them to only be started if necessary. If the user has chosen
to keep the display on and not-dimmed all the time, the tickers can't
start as their tick value must be a positive integer.

* feat(display.go): stop tickers when auto-dim/auto-off is disabled

* feat(rpc): implement display backlight control methods

* feat(ui): implement display backlight control

* chore: update variable names

As part of @joshuasing's review on #17, updated variables & constants to
match the Go best practices.

Signed-off-by: Cameron Fleming <cameron@nevexo.space>

* fix(display): move backlightTicker setup into screen setup goroutine

Signed-off-by: Cameron Fleming <cameron@nevexo.space>

* chore: fix some start-up timing issues

* fix(display): Don't attempt to start the tickers if the display is disabled

If max_brightness is zero, then there's no point in trying to dim it (or
turn it off...)

* fix: wakeDisplay() doesn't need to stop the tickers

The tickers only need to be reset, if they're disabled, they won't have
been started.

* fix: Don't wake up the display if it's turned off

---------

Signed-off-by: Cameron Fleming <cameron@nevexo.space>

config.go

@@ -12,24 +12,30 @@ type WakeOnLanDevice struct {
 }
 
 type Config struct {
-	CloudURL          string            `json:"cloud_url"`
-	CloudToken        string            `json:"cloud_token"`
-	GoogleIdentity    string            `json:"google_identity"`
-	JigglerEnabled    bool              `json:"jiggler_enabled"`
-	AutoUpdateEnabled bool              `json:"auto_update_enabled"`
-	IncludePreRelease bool              `json:"include_pre_release"`
-	HashedPassword    string            `json:"hashed_password"`
-	LocalAuthToken    string            `json:"local_auth_token"`
-	LocalAuthMode     string            `json:"localAuthMode"` //TODO: fix it with migration
-	WakeOnLanDevices  []WakeOnLanDevice `json:"wake_on_lan_devices"`
+	CloudURL             string            `json:"cloud_url"`
+	CloudToken           string            `json:"cloud_token"`
+	GoogleIdentity       string            `json:"google_identity"`
+	JigglerEnabled       bool              `json:"jiggler_enabled"`
+	AutoUpdateEnabled    bool              `json:"auto_update_enabled"`
+	IncludePreRelease    bool              `json:"include_pre_release"`
+	HashedPassword       string            `json:"hashed_password"`
+	LocalAuthToken       string            `json:"local_auth_token"`
+	LocalAuthMode        string            `json:"localAuthMode"` //TODO: fix it with migration
+	WakeOnLanDevices     []WakeOnLanDevice `json:"wake_on_lan_devices"`
 	EdidString        string            `json:"hdmi_edid_string"`
+  DisplayMaxBrightness int               `json:"display_max_brightness"`
+	DisplayDimAfterSec   int               `json:"display_dim_after_sec"`
+	DisplayOffAfterSec   int               `json:"display_off_after_sec"`
 }
 
 const configPath = "/userdata/kvm_config.json"
 
 var defaultConfig = &Config{
-	CloudURL:          "https://api.jetkvm.com",
-	AutoUpdateEnabled: true, // Set a default value
+	CloudURL:             "https://api.jetkvm.com",
+	AutoUpdateEnabled:    true, // Set a default value
+	DisplayMaxBrightness: 64,
+	DisplayDimAfterSec:   120,  // 2 minutes
+	DisplayOffAfterSec:   1800, // 30 minutes
 }
 
 var config *Config