feat(history): nodb backlog (#114)

Implements all open items from the nodb backlog:

statusbar
- PREF_STATUSBAR_SHOW_DBBACKEND (default ON) gates the [sqlite] /
  [flatfile] indicator; toggle via "/statusbar show|hide dbbackend"

/history off|on
- "/history off" now stops persistence as well as hiding history on
  open: sets PREF_DBLOG=off + PREF_CHLOG=false in addition to
  PREF_HISTORY=false
- "/history on" restores persistence (re-enabling PREF_DBLOG=on if
  it was off) and PREF_CHLOG, in addition to PREF_HISTORY=true

/logging
- Removed the "/logging chat on|off" subcommand — chat-log
  persistence is now controlled exclusively by /history; the
  command kept only "/logging group on|off" for MUC logs
- All "use '/logging chat on' to enable" hints replaced with
  "/history on"

/privacy logging
- Single-pass validation across {on, off, redact, flatfile}
- Backend-switching values (on, flatfile) now take effect
  immediately when connected (via log_database_switch_backend),
  matching "/history switch" behaviour; off/redact only flip
  pref bits and keep the live backend open
- Updated help text to reflect runtime switching

/correction off
- win_print_outgoing and win_print_outgoing_with_receipt now gate
  _win_correct on PREF_CORRECTION_ALLOW, matching incoming-msg
  paths. Previously a peer's correction reflected via XEP-0280
  carbons (or the user's own /correct invocation) was applied
  in-buffer regardless of the pref

style
- Two local g_strndup allocations in database_flatfile.c switched
  from char* with manual g_free to auto_gchar gchar*

src/command/cmd_defs.c

@@ -1289,8 +1289,8 @@ static const struct cmd_t command_defs[] = {
       CMD_TAGS(
               CMD_TAG_UI)
       CMD_SYN(
-              "/statusbar show name|number|read",
-              "/statusbar hide name|number|read",
+              "/statusbar show name|number|read|dbbackend",
+              "/statusbar hide name|number|read|dbbackend",
               "/statusbar maxtabs <value>",
               "/statusbar tablen <value>",
               "/statusbar tabmode default|dynamic|actlist",
@@ -1308,6 +1308,7 @@ static const struct cmd_t command_defs[] = {
               { "show|hide name", "Show or hide names in tabs." },
               { "show|hide number", "Show or hide numbers in tabs." },
               { "show|hide read", "Show or hide inactive tabs." },
+              { "show|hide dbbackend", "Show or hide the database backend indicator [sqlite] or [flatfile]." },
               { "self user|barejid|fulljid", "Show account user name, barejid, fulljid as status bar title." },
               { "self off", "Disable showing self as status bar title." },
               { "chat user|jid", "Show users name, or fulljid. Change needs a redraw/restart to take effect." },
@@ -1664,17 +1665,13 @@ static const struct cmd_t command_defs[] = {
       CMD_TAGS(
               CMD_TAG_CHAT)
       CMD_SYN(
-              "/logging chat|group on|off")
+              "/logging group on|off")
       CMD_DESC(
-              "Configure chat logging. "
-              "Switch logging on or off. "
-              "Chat logging will be enabled if /history is set to on. "
-              "When disabling this option, /history will also be disabled. ")
+              "Configure groupchat (MUC) logging. "
+              "Regular chat logging is controlled by /history.")
       CMD_ARGS(
-              { "chat on|off", "Enable/Disable regular chat logging." },
               { "group on|off", "Enable/Disable groupchat (room) logging." })
       CMD_EXAMPLES(
-              "/logging chat on",
               "/logging group off")
     },
 
@@ -1888,15 +1885,16 @@ static const struct cmd_t command_defs[] = {
               "/history export [<jid>]",
               "/history import [<jid>]")
       CMD_DESC(
-              "Switch chat history on or off, /logging chat will automatically be enabled when this setting is on. "
-              "When history is enabled, previous messages are shown in chat windows. "
+              "Enable or disable chat history. "
+              "When on, messages are persisted via the active database backend and shown in chat windows. "
+              "When off, persistence stops and old history is hidden on chat-window open. "
               "Use 'backend' to show the active database backend. "
               "Use 'switch' to change the active database backend at runtime without reconnecting. "
               "Use 'verify' to check integrity of stored message history. "
               "Use 'export' to copy messages from SQLite to flat-file format, or 'import' to copy from flat-file to SQLite. "
               "Both export and import merge with existing data (duplicates are skipped).")
       CMD_ARGS(
-              { "on|off", "Enable or disable showing chat history." },
+              { "on|off", "Enable or disable persistence and showing chat history." },
               { "backend", "Show the name of the active database backend." },
               { "switch sqlite|flatfile", "Switch the active database backend at runtime." },
               { "verify [<jid>]", "Verify integrity of message history. Optionally specify a JID to check only one contact." },
@@ -2741,7 +2739,7 @@ static const struct cmd_t command_defs[] = {
               "clientid to set the client identification name "
               "session_alarm to configure an alarm when more clients log in.")
       CMD_ARGS(
-              { "logging on|redact|off|flatfile", "Switch chat logging. 'on' uses SQLite database (default). 'flatfile' stores messages as plain text files in ~/.local/share/profanity/flatlog/ that can be manually edited with any text editor. 'off' disables logging entirely. 'redact' stores messages with content replaced by '[redacted]'. Note: 'off' might have unintended consequences, such as not being able to decrypt OMEMO encrypted messages received later via MAM. The 'flatfile' setting takes effect on next connection." },
+              { "logging on|redact|off|flatfile", "Switch chat logging backend. 'on' uses the SQLite database (default). 'flatfile' stores messages as plain-text files under ~/.local/share/profanity/flatlog/ that can be edited with any text editor. 'off' disables logging entirely. 'redact' keeps logging but replaces every message body with '[REDACTED]'. Note: 'off' may have side effects such as not being able to decrypt OMEMO messages received later via MAM. Backend changes ('on' / 'flatfile') take effect immediately when connected, otherwise on next connect." },
               { "os on|off", "Choose whether to include the OS name if a user asks for software information (XEP-0092)." }
               )
       CMD_EXAMPLES(