refactor(db): finish #1283 — Option 4: ingestor owns neighbor-graph + schema migrations; server is read-only (fixes #1287) (#1289)

Red commit:
https://github.com/Kpa-clawbot/CoreScope/commit/eae179b99b5fd34924547632aa8f8025c405aa53
(CI: pending — opens with this PR)

Finishes #1283. RED test `TestServerSourceHasNoCachedRWCalls` goes from
failing (13 writer call-sites) to GREEN (zero). Per #1287 Option 4
(https://github.com/Kpa-clawbot/CoreScope/issues/1287#issuecomment-4485099992):
ingestor owns the neighbor graph build + persist; server reads the
snapshot.

**Category A — Schema migrations** → new `internal/dbschema` package.
`dbschema.Apply(rw)` runs in `cmd/ingestor` startup (in `OpenStore`).
`dbschema.AssertReady(ro)` runs in `cmd/server/main.go` and
FATAL-LOG-EXITS if any expected column/index/table is missing — the
operator must restart the ingestor first. Covers indexes,
`neighbor_edges`, `observations.resolved_path`,
`observers.{inactive,last_packet_at,iata}`,
`(inactive_)nodes.foreign_advert`, `transmissions.from_pubkey`.

**Category B — Backfill** → ingestor.
`BackfillFromPubkey` and observer-blacklist soft-delete moved to
`cmd/ingestor/maintenance.go`. Server keeps an inert
`fromPubkeyBackfillSnapshot` stub for `/api/healthz` API compatibility.

**Category C — Neighbor-graph persistence (Option 4)** → ingestor
writes, server reads.
- Ingestor (`cmd/ingestor/neighbor_builder.go`): every 60s scans
`observations + transmissions`, extracts edges (originator↔first-hop for
ADVERTs; observer↔last-hop for all), resolves hop prefixes via a
node-table prefix index, upserts into `neighbor_edges`.
- Server (`cmd/server/neighbor_recomputer.go`): every 60s re-reads
`neighbor_edges` and atomic-swaps the resulting `NeighborGraph` into
`s.graph`. Initial load is synchronous on startup. All server-side
incremental edge writers (the two `asyncPersistResolvedPathsAndEdges`
paths in `cmd/server/store.go`) are gone.
- Neighbor-edge daily prune (`PruneNeighborEdges`) moved to ingestor.

**Why Option 4**: clean read/write separation, no startup CPU spike
(server loads existing snapshot instead of rebuilding from history), no
IPC/delta-protocol churn. Staleness budget ~60s — same model as the
analytics recomputers in #1240 / #1248 / #672 axis 2.

**Recomputer interval default for neighbor graph**: 60s
(`NeighborGraphRecomputerDefaultInterval`,
`NeighborEdgesBuilderInterval`).

**Invariants added**:
- `TestServerSourceHasNoCachedRWCalls` (RED commit eae179b9): grep
enforces zero `cachedRW(`, `mode=rw`, or `sql.Open(_journal_mode=WAL…)`
in non-test `cmd/server/` sources.
- `TestServerStartupRequiresMigratedSchema`: server refuses to start
against an unmigrated DB.
- `TestNeighborGraphRecomputerLoadsSnapshot`: post-write snapshot is
picked up on the next refresh.
- `TestNeighborEdgesBuilderUpsertsFromObservations`: end-to-end pipeline
writes the expected edge.

`grep cachedRW cmd/server/*.go | grep -v _test.go` → 0 matches.

Fixes #1287.

---------

Co-authored-by: MeshCore Bot <bot@meshcore.local>
Co-authored-by: Kpa-clawbot <Kpa-clawbot@users.noreply.github.com>
Co-authored-by: corescope-bot <bot@corescope.local>

.github/workflows/deploy.yml

@@ -191,6 +191,12 @@ jobs:
           go build -o ../../corescope-server .
           echo "Go server built successfully"
 
+      - name: Build Go migrate tool
+        run: |
+          cd cmd/migrate
+          go build -o ../../corescope-migrate .
+          echo "Go migrate tool built successfully"
+
       - name: Install npm dependencies
         run: npm ci --production=false
 
@@ -205,6 +211,15 @@ jobs:
       - name: Freshen fixture timestamps
         run: bash tools/freshen-fixture.sh test-fixtures/e2e-fixture.db
 
+      - name: Migrate fixture DB to current schema (#1287)
+        # Server now ASSERTs schema is migrated and refuses to start
+        # otherwise (cmd/server/main.go: dbschema.AssertReady). In prod
+        # the ingestor owns dbschema.Apply, but CI starts only the
+        # server against the committed e2e fixture — so we run the
+        # standalone migrate tool here to bring the fixture up to the
+        # required shape before the server boots.
+        run: ./corescope-migrate -db test-fixtures/e2e-fixture.db
+
       - name: Start Go server with fixture DB
         run: |
           fuser -k 13581/tcp 2>/dev/null || true