docs: split 593-line README into focused top page + docs/

[vr000m]

Summary

The README had grown to 593 lines, burying install/run basics under protocol, deployment, integration, and migration detail. This splits it so the top page stays focused on why it exists + install + run, and the deeper material moves to thematic files under docs/.

README keeps: preamble (why it exists), V1 scope, Running the server, Managing agents with just, Choosing a backend and model, and a new Documentation index. 593 → ~190 lines.

Moved verbatim to docs/:

File	Content
docs/operations.md	Multi-backend operation, per-ASR socket convention, two-agent install, A/B benchmark, checking server health, Whisper hallucination-suppression knobs
docs/integration.md	Client usage, Pipecat integration, Reference consumer (Koda)
docs/protocol.md	Protocol subset (V1 wire events)
docs/migration.md	Upgrading 0.1.x → 0.2.0

Per request, the just operator recipes stay on the top page (promoted to their own ## Managing agents with just); only the per-ASR reference table they cite moved (link repointed).

Verification

• No content lost: comm diff of original README vs the union of all new files shows only the 12 lines I deliberately changed — 4 re-leveled headings + 8 repointed cross-references. Everything else is byte-identical (extracted with sed, not retyped).
• All links resolve: a script checks every internal markdown link + heading anchor across the 5 files — README → docs, docs → docs, and same-file anchors all pass.
• No stale external refs: nothing else in the repo links to the moved README sections.

Docs-only — no code changes.