v0.4.0 — human-readable metadata catalog + GET /metadata New feature, backwards compatible. Adds GET /metadata returning a static catalog of every indicator, signal, and level the compute endpoint emits, with human labels, descriptions, interpretation hints, units, and categories. Consumers fetch once on startup; cache invalidates on version bump. Includes lookup(path) helper with three-tier fallback (exact -> strip array indices -> bare leaf) so dynamic dot-paths like retracements[42].Direction or prevTimeframe.rsi still resolve. Covers all ~70 top-level registry indicators plus nested object fields for SMC events, retracements, sessions, and divergences. 321 unit tests passing (11 new metadata tests).