feat: add silent NTP time sync on boot via saved WiFi credentials

New "Auto Sync on Boot" toggle in Clock Settings. When enabled, a
background FreeRTOS task scans for saved WiFi networks at boot,
connects, syncs time via NTP, then tears down WiFi — all without
blocking boot or requiring user interaction. If no saved network is
found after two scan attempts (with a 3-second retry gap), it bails
silently.

Conflict guards (BootNtpSync::cancel()) added to all WiFi-using
activities so the background task cleans up before any user-initiated
WiFi flow. Also fixes clock not appearing in the header until a button
press by detecting the invalid→valid time transition after NTP sync.

Made-with: Cursor

lib/I18n/translations/czech.yaml

@@ -343,3 +343,4 @@ STR_INDEXING_STATUS_TEXT: "Text stavového řádku"
 STR_INDEXING_STATUS_ICON: "Ikona stavového řádku"
 STR_SYNC_CLOCK: "Sync Clock"
 STR_TIME_SYNCED: "Time synced!"
+STR_AUTO_NTP_SYNC: "Auto Sync on Boot"

lib/I18n/translations/english.yaml

@@ -364,6 +364,7 @@ STR_INDEXING_STATUS_TEXT: "Status Bar Text"
 STR_INDEXING_STATUS_ICON: "Status Bar Icon"
 STR_SYNC_CLOCK: "Sync Clock"
 STR_TIME_SYNCED: "Time synced!"
+STR_AUTO_NTP_SYNC: "Auto Sync on Boot"
 STR_MANAGE_BOOK: "Manage Book"
 STR_ARCHIVE_BOOK: "Archive Book"
 STR_UNARCHIVE_BOOK: "Unarchive Book"

lib/I18n/translations/french.yaml

@@ -343,3 +343,4 @@ STR_INDEXING_STATUS_TEXT: "Texte barre d'état"
 STR_INDEXING_STATUS_ICON: "Icône barre d'état"
 STR_SYNC_CLOCK: "Sync Clock"
 STR_TIME_SYNCED: "Time synced!"
+STR_AUTO_NTP_SYNC: "Auto Sync on Boot"

lib/I18n/translations/german.yaml

@@ -343,3 +343,4 @@ STR_INDEXING_STATUS_TEXT: "Statusleistentext"
 STR_INDEXING_STATUS_ICON: "Statusleistensymbol"
 STR_SYNC_CLOCK: "Sync Clock"
 STR_TIME_SYNCED: "Time synced!"
+STR_AUTO_NTP_SYNC: "Auto Sync on Boot"

lib/I18n/translations/portuguese.yaml

@@ -343,3 +343,4 @@ STR_INDEXING_STATUS_TEXT: "Texto da barra"
 STR_INDEXING_STATUS_ICON: "Ícone da barra"
 STR_SYNC_CLOCK: "Sync Clock"
 STR_TIME_SYNCED: "Time synced!"
+STR_AUTO_NTP_SYNC: "Auto Sync on Boot"

lib/I18n/translations/romanian.yaml

@@ -318,3 +318,4 @@ STR_EMBEDDED_STYLE: "Stil încorporat"
 STR_OPDS_SERVER_URL: "URL server OPDS"
 STR_SYNC_CLOCK: "Sync Clock"
 STR_TIME_SYNCED: "Time synced!"
+STR_AUTO_NTP_SYNC: "Auto Sync on Boot"

lib/I18n/translations/russian.yaml

@@ -343,3 +343,4 @@ STR_INDEXING_STATUS_TEXT: "Текст в строке"
 STR_INDEXING_STATUS_ICON: "Иконка в строке"
 STR_SYNC_CLOCK: "Sync Clock"
 STR_TIME_SYNCED: "Time synced!"
+STR_AUTO_NTP_SYNC: "Auto Sync on Boot"

lib/I18n/translations/spanish.yaml

@@ -343,3 +343,4 @@ STR_INDEXING_STATUS_TEXT: "Texto barra estado"
 STR_INDEXING_STATUS_ICON: "Icono barra estado"
 STR_SYNC_CLOCK: "Sync Clock"
 STR_TIME_SYNCED: "Time synced!"
+STR_AUTO_NTP_SYNC: "Auto Sync on Boot"

lib/I18n/translations/swedish.yaml

@@ -343,3 +343,4 @@ STR_INDEXING_STATUS_TEXT: "Statusfältstext"
 STR_INDEXING_STATUS_ICON: "Statusfältsikon"
 STR_SYNC_CLOCK: "Sync Clock"
 STR_TIME_SYNCED: "Time synced!"
+STR_AUTO_NTP_SYNC: "Auto Sync on Boot"