Log files source: follow the logs of Traefik, nginx and other programs

Files source (source_type=file), declared in Settings > Log sources > Log
files (/data/files.json, 50 at most): name (= app), path as mounted in the
container (file or glob, rotated copies .1/.gz left out, 200 files per
glob), format, optional host, switch.

- formats: plain text (level detected, leading timestamp read and removed),
  JSON lines (msg/time/level keys, numeric pino levels, other keys as
  fields, nested ones dotted), logfmt, access log CLF (nginx, Apache,
  Traefik CLF with router/backend/duration), Traefik access log in JSON
  (summary "GET host/path 200 · 12.5 ms · router · client"), regular
  expression with named groups time/level/msg/host/app/status; 5xx = err,
  4xx = warning; fields named like LogStream's own renamed field_<name>
- indented lines (text) and non-matching lines (regex) added to the
  previous entry, which waits 2 s for them
- inode + offset per file in /data/files-state.json, rotation (end of
  .1 read first), copytruncate, file renamed within the glob; last
  FILES_BACKFILL (1h) of dated lines read when turned on, new files read
  from their start
- status per file (files followed, entries read, not found / permission)

UI: rows with switch, name, path, format, host (regex field when needed),
status line; green edge, tint and FILE badge in the list, "Files" in the
source filter, HTTP fields first in the details, FR/EN. docker-compose,
.env.example and README (EN/FR): mounts, formats, FILES_BACKFILL.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

query.go

@@ -119,10 +119,10 @@ func (f Filter) filterExpr() string {
 		parts = append(parts, "app:="+strconv.Quote(f.App))
 	}
 	switch f.Source {
-	case "docker", "host", "kernel", "audit", "logstream":
+	case "docker", "host", "kernel", "audit", "logstream", "file":
 		parts = append(parts, `source_type:=`+strconv.Quote(f.Source))
 	case "syslog": // also matches logs stored before source_type existed
-		parts = append(parts, `!(source_type:in("docker","host","kernel","audit","logstream"))`)
+		parts = append(parts, `!(source_type:in("docker","host","kernel","audit","logstream","file"))`)
 	}
 	if f.Severity >= 0 && f.Severity < 7 {
 		names := make([]string, 0, 8)