feat(sat): generate the frequency plan, and join on the catalog number

25 satellites, typed by hand and never revisited. Eight of them were the
first-generation Tevel constellation, which re-entered in 2024; four more had
come down too; and the nine Tevel-2 satellites that replaced them, the Chinese
space station, AO-27, AO-123 and twenty others were simply absent. So: 44
satellites now, and a generator instead of a memory.

cmd/satgen joins three public sources on the NORAD catalog number — Celestrak's
amateur group and PE0SAT's mirror for which birds OpsLog can actually get
elements for, and SatNOGS DB for the transmitters. It is a one-shot tool, run by
hand, the same arrangement as cmd/cntygen, and it is deliberately conservative:

  - It never destroys a curated entry. The hand-written plans hold things
    SatNOGS does not reliably carry — a CTCSS tone, the QO-100 passband as
    operators describe it — so an existing bird keeps its data and only gains
    its catalog number.
  - It prunes on the re-entry date, which is a fact SatNOGS publishes rather
    than a judgement about which of the missing satellites are missing for good.
  - It refuses a digital uplink that does not say what it is. A GMSK uplink is a
    command channel far more often than a digipeater, and shipping the wrong one
    invites somebody to transmit on a control frequency. An analog uplink with
    both ends is a contact by construction, which is what catches the repeaters
    that describe themselves only as "Mode V/U FM".
  - Its output is deterministic. One satellite can hold two catalog entries —
    GreenCube is 53106 in one feed and 53109 in the other — and iterating a map
    picked a different one each run.

A bird now carries its NORAD number, and that is how its elements are found.
Names were the only join before, and they are written differently by every party
involved: "TIANYAN 01" and "TO-108" are one satellite that had never once met,
so TO-108 tracked nothing at all.

And the plan now reaches a station that has already run OpsLog. The editable
copy was written on the first launch and was the operator's list for ever after,
so a release adding nine satellites reached nobody who had opened the tab. It is
merged on each load instead: a satellite they already have is untouched, edits
and corrections included, and only the ones they have never seen are added.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

internal/sat/sat.go

@@ -186,6 +186,27 @@ func (s *Store) Get(name string) (Element, bool) {
 	return e, ok
 }
 
+// GetNORAD returns one satellite's elements by catalog number.
+//
+// The exact join, and the only one that stays exact. A name is written
+// differently by every party involved — the feed says "RADFXSAT (FOX-1B)", the
+// operator says "AO-91", AMSAT's chart says both — and matching on letters and
+// digits gets most of them and quietly misses the rest. The catalog number is
+// in the TLE itself and is what a frequency plan should carry.
+func (s *Store) GetNORAD(n int) (Element, bool) {
+	if n <= 0 {
+		return Element{}, false
+	}
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	for _, k := range s.order {
+		if e := s.byKey[k]; e.NORAD == n {
+			return e, true
+		}
+	}
+	return Element{}, false
+}
+
 // Names lists what the store holds, in the order it arrived.
 func (s *Store) Names() []string {
 	s.mu.RLock()