fix(packets): order by ingest id, not rxTime — fresh activity visible on packets page (#1345)

[Kpa-clawbot]

Summary

Fixes #1345 — the packets page shows "no recent activity" while MQTT ingest is healthy because the default /api/packets query was ORDER BY first_seen DESC, and PR #1233 redefined first_seen as the observer's radio receive time (rxTime). When an observer buffers offline and uploads hours later, its packets land with hours-old first_seen values; older-ingested packets with fresher rxTime then crowd the top of the list and the visually freshest activity disappears.

Fix

Switch the default ordering to t.id DESC (ingest order) on /api/packets and the closely-related endpoints. id is monotonic with ingest time and immune to buffered uploads.

Endpoints changed (all use the same fix for the same reason):

Path	Function	File
GET /api/packets (default)	DB.QueryPackets, Store.QueryPackets	cmd/server/db.go, cmd/server/store.go
GET /api/packets?nodes=…	DB.QueryMultiNodePackets, Store.QueryMultiNodePackets	same
Node detail "recent transmissions"	DB.GetRecentTransmissionsForNode	cmd/server/db.go

since= semantic — preserved

since= still filters by first_seen (RFC3339 path uses the observations.timestamp subquery), i.e. "packets the network received since X." Buffered uploads of older packets are still excluded from a since=15m view even if they were ingested in the last 15 minutes. Only the display order changes; filtering by receive time is unchanged.

Audit — NOT changed

• Store.QueryGroupedPackets already sorts by LatestSeen (max observation timestamp), which is correct for the grouped view and immune to the buffered-upload regression.
• GetChannelMessages and channel sample_json subqueries keep first_seen DESC — channel message chronology is meaningful for message UX; if buffered uploads become a problem here too it's a separate UX call (out of scope for bug(packets): page shows old/empty because first_seen=rxTime sorts buffered uploads to top — should order by ingest-time #1345).
• s.packets insertion ordering (Load + ingest) — untouched. The fix sorts at query time so we don't perturb oldestLoaded invariants.

Tests — TDD red → green

• Red: 508f4371 adds cmd/server/packets_order_test.go with two cases — order assertion (failed on master with [fresh, buffered]) and since-filter semantic (RFC3339 path uses observation timestamps).
• Green: 0fd685e7 switches the SQL + in-memory ordering. Tests pass; full cmd/server suite green locally (44s).

Out of scope

• Re-thinking fix: ingestor uses ingest-time now() instead of observer receive time #1233's first_seen semantics
• Adding a UI sort toggle (issue's option 2)
• Channel-message page ordering

Preflight

Clean (bash ~/.openclaw/skills/pr-preflight/scripts/run-all.sh origin/master).