feat(graph): add metadata storage and lookup for entity matching

[mfiedorowicz]

Add support for storing and querying entity metadata in graph_nodes table, enabling correlation-based entity matching with fallback mechanisms.

Key changes:

• Add metadata JSONB column with GIN index for efficient lookups
• Add content_hash column as last-resort matching fallback
• Implement matching priority: diode_id -> source_match keys -> field-based -> content_hash
• Store source_match.diode_id (equals externalID) for direct lookups
• Preserve original client metadata in snapshots for audit trail

Database:

• Migration 20260203000001: add metadata column
• Migration 20260203000002: add content_hash column
• New queries: FindNodeByMetadata, FindNodeByContentHash

Code quality:

• Fix error shadowing bug in upsertNode
• Remove unnecessary struct copy in maybeUpdateNodeSchema
• Add ContentHashMatchConfidence constant
• Increase matching package test coverage to 94%

🤖

[github-actions]

Go test coverage

STATUS	ELAPSED	PACKAGE	COVER	PASS	FAIL	SKIP
🟢 PASS	1.54s	github.com/netboxlabs/diode/diode-server/auth	44.7%	42	0	0
🟢 PASS	1.12s	github.com/netboxlabs/diode/diode-server/auth/cli	0.0%	0	0	0
🟢 PASS	1.03s	github.com/netboxlabs/diode/diode-server/authutil	82.8%	5	0	0
🟢 PASS	0.12s	github.com/netboxlabs/diode/diode-server/dbstore/postgres	0.0%	0	0	0
🟢 PASS	1.08s	github.com/netboxlabs/diode/diode-server/entityhash	86.7%	16	0	0
🟢 PASS	1.22s	github.com/netboxlabs/diode/diode-server/entitymatcher	83.0%	91	0	0
🟢 PASS	0.25s	github.com/netboxlabs/diode/diode-server/errors	0.0%	0	0	0
🟢 PASS	1.29s	github.com/netboxlabs/diode/diode-server/ingester	82.7%	25	0	0
🟢 PASS	1.13s	github.com/netboxlabs/diode/diode-server/matching	94.1%	66	0	0
🟢 PASS	1.07s	github.com/netboxlabs/diode/diode-server/migrator	70.4%	4	0	0
🟢 PASS	4.17s	github.com/netboxlabs/diode/diode-server/netboxdiodeplugin	83.6%	40	0	0
🟢 PASS	0.17s	github.com/netboxlabs/diode/diode-server/pprof	0.0%	0	0	0
🟢 PASS	2.66s	github.com/netboxlabs/diode/diode-server/reconciler	58.9%	147	0	0
🟢 PASS	1.02s	github.com/netboxlabs/diode/diode-server/reconciler/applier	85.7%	1	0	0
🟢 PASS	0.12s	github.com/netboxlabs/diode/diode-server/reconciler/changeset	0.0%	0	0	0
🟢 PASS	1.10s	github.com/netboxlabs/diode/diode-server/reconciler/differ	63.8%	6	0	0
🟢 PASS	1.02s	github.com/netboxlabs/diode/diode-server/server	85.7%	14	0	0
🟢 PASS	1.01s	github.com/netboxlabs/diode/diode-server/strcase	100.0%	24	0	0
🟢 PASS	1.04s	github.com/netboxlabs/diode/diode-server/telemetry	28.0%	26	0	0
🟢 PASS	1.04s	github.com/netboxlabs/diode/diode-server/telemetry/otel	91.7%	25	0	0
🟢 PASS	0.15s	github.com/netboxlabs/diode/diode-server/tls	0.0%	0	0	0
🟢 PASS	1.01s	github.com/netboxlabs/diode/diode-server/version	100.0%	2	0	0

Total coverage: 57.9%

[jajeffries]

Overall looks good 👍