schema: implement interface_type lookup table with seed data

[AlbinoGeek]

Parent: #8 — Additional Performance Metrics

Implement the interface_type lookup table as ratified in #8 (schema finalized 182139ZMAY26, names approved 200636ZMAY26).

Schema

CREATE TABLE interface_type (
    interface_type_id   SERIAL PRIMARY KEY,
    bandwidth_peak_gb_s FLOAT NOT NULL,
    description         TEXT NOT NULL,        -- "PCIe 4.0 x16", "SXM5", "Thunderbolt 4"
    interface_family    TEXT NULLABLE,         -- "PCIe", "SXM", "CXL", "NVLink", "USB", "OCuLink"
    transfer_rate       INT NULLABLE,          -- PCIe: GT/s per lane (e.g. 16 for Gen4); null for non-PCIe
    lane_count          INT NULLABLE           -- PCIe: lane width (e.g. 16); null for non-PCIe
);

Seed data required

Pre-seed rows for common well-known interface types, including at minimum:

• PCIe Gen 1–5 × x1 / x4 / x8 / x16 (peak bandwidth computed from standard spec)
• SXM2 / SXM4 / SXM5
• NVLink 2.0 / 3.0 / 4.0 (reserved — interface_family = "NVLink", no FK references yet per Phase 1 decision)
• Thunderbolt 3 / 4
• OCuLink 2.0

No pre-seeded rows for degraded states — display layer constructs degradation descriptions at runtime from the two FK interface_type rows (slot_native and actual).

Acceptance criteria

• Migration creates interface_type with correct column types and NOT NULL constraints
• Seed migration inserts well-known rows (PCIe Gen 1–5 variants at minimum)
• bandwidth_peak_gb_s values match published specs for each seeded row
• Rows for NVLink are seeded with interface_family = "NVLink" but not yet FK-referenced by any other table
• Migration is reversible (down path defined)

Notes

transfer_rate and lane_count are nullable to accommodate non-PCIe interfaces (SXM, NVLink, USB). Bandwidth is the universal comparable field. For PCIe, bandwidth_peak_gb_s = transfer_rate × lane_count × 2 / 8 (bidirectional, GB/s).

— Bastion