Store a target's settings as columns (closes #543)

A target's settings move from the per-type JSON string in
targets.config to columns: url, headers, timeout_seconds,
forward_query, archive_expiry and archive_rotation. A column a type
does not use stays empty. headers holds the header map as JSON text
through GORM's JSON serializer, and archive_expiry holds a
time.Duration, 0 meaning never, so nothing that reads a target parses
it. The forms check each setting once, with the same refusals and
messages, and the edit form is filled from the columns, so the
per-type config structs, their parsers and the "could not be read"
branches are gone. A delivery task carries the six settings in place
of the JSON string.

Model: opus-5-5

internal/delivery/target_headers.go

@@ -17,7 +17,7 @@ import (
 const MaxTargetTimeoutSeconds = 300
 
 // Errors returned when a target's header or timeout form input
-// cannot be turned into a configuration.
+// cannot be turned into the target's setting.
 //
 // None of these ever quotes a header VALUE. A target header value
 // is routinely an authorization token, and these messages are shown
@@ -48,8 +48,8 @@ var (
 )
 
 // isReservedTargetHeader reports whether name (canonicalised) is a
-// header a target configuration may not set, because the delivery
-// path or net/http itself writes it regardless.
+// header a target may not set, because the delivery path or
+// net/http itself writes it regardless.
 //
 // These are rejected rather than accepted-and-ignored. Storing a
 // header that provably never reaches the wire tells the operator
@@ -77,13 +77,11 @@ func isReservedTargetHeader(name string) bool {
 
 // ParseTargetHeaders turns the target form's headers field — one
 // "Name: value" pair per line, blank lines ignored — into the map
-// stored in HTTPTargetConfig.Headers. Names are canonicalised, so a
+// stored in database.Target.Headers. Names are canonicalised, so a
 // name repeated in a different case is still a duplicate rather than
 // one pair silently overwriting the other.
 //
-// An input with no pairs yields an empty map, which omitempty drops
-// from the stored config, so a target configured with no headers
-// stores no headers key at all.
+// An input with no pairs yields an empty map.
 func ParseTargetHeaders(raw string) (map[string]string, error) {
 	headers := make(map[string]string)
 
@@ -223,8 +221,8 @@ func FormatTargetHeaders(headers map[string]string) string {
 
 // ParseTargetTimeout interprets the target form's timeout field as
 // a whole number of seconds. An empty field means "unset" and yields
-// 0, which omitempty drops from the stored config and which the
-// delivery path reads as "use the shared client's timeout".
+// 0, which the delivery path reads as "use the shared client's
+// timeout".
 //
 // Anything else that is not a whole number in range is an error, not
 // a silently substituted default: a target whose timeout was typed