## Summary
Adds a sortable **First Seen** column to the Nodes table so users can
spot newly observed repeaters in their region (per the reporter's use
case).
Closes#1166
## Backend
`/api/nodes` already exposes `first_seen` per node via `db.scanNodeRow`
(sourced from the existing `nodes.first_seen` column — no schema
migration, no recomputation, no extra query cost). The red test pins
that contract.
## Frontend (`public/nodes.js`)
- New `<th data-sort-key="first_seen" data-sort-default="desc">First
Seen</th>` between Last Seen and Adverts.
- Cell renders via `renderNodeTimestampHtml(n.first_seen)` — same
relative-time + absolute-ISO `title=` tooltip as the Last Seen column.
Empty values render as `—`.
- `sortNodes` gains a `first_seen` branch with **empty-last** semantics:
nodes without a `first_seen` always sort to the bottom regardless of
asc/desc direction, so unknowns never clutter the top of the table.
- Empty-state `colspan` bumped 7 → 8.
## TDD
- **Red commit** `112442f4` — `test-issue-1166-first-seen-column.js` +
`cmd/server/first_seen_1166_test.go`. The backend half passes on red
(field already returned); 5 frontend assertions fail on assertions
(column header missing, sort branch missing, empty-last violated).
- **Green commit** `9274b36c` — only `public/nodes.js`. All 6 tests
pass.
Verified red is real-fail (assertion-shaped) by checking out the red
commit's `nodes.js` and re-running the test: 5 failures, all on
`assert.strictEqual`, none on parse/import.
## Test results
```
node test-issue-1166-first-seen-column.js → 6 passed, 0 failed
node test-frontend-helpers.js → 611 passed, 0 failed
go test ./cmd/server/... → ok (45.16s, all pass)
```
## Files changed
- `public/nodes.js` (+14 / −1)
- `test-issue-1166-first-seen-column.js` (new)
- `cmd/server/first_seen_1166_test.go` (new)
## Scope guardrails
- No schema migration.
- No new files outside the worktree's three allowed surfaces.
- No refactor of other Nodes columns.
- Empty cells handled in both render (em-dash) and sort (always last).
---------
Co-authored-by: fix-1166-bot <bot@corescope.local>
