docs(lethe-web-ui-foundation): import design handoff, add task file

Bring in the React prototype bundle from the claude-design handoff
(`docs/design_handoff_assistant_log/`) and the new task file
(`docs/tasks/lethe-web-ui-foundation.md`) covering the foundation slice
of the assistant-log web UI: scaffold, embed pipeline, shell, Home, and
Session view. Backend additions to `/api/v1/sessions` (summary,
turn_count, token totals, model) are part of this task; Projects, Stats,
Search, Health, and Settings are split into deferred sibling tasks.

docs(lethe-server): record verify section, mark Verified

docs(task): record execution conclusion across all 9 phases

feat(cmd): wire server with /healthz /readyz /metrics + authed /api/v1

Phase 9 of lethe-server: thin main.go that loads config, registers every
steward asset, and orchestrates Inject -> Init -> Start -> wait -> Stop ->
Destroy. Compensates for the Phase 4 finding (steward.Manager does not
unwind on Init failure) by tracking destroyer-implementing assets in a
parallel slice and invoking Destroy in reverse registration order with a
per-call timeout when Init or Start fails.

Server.Start now opens its TCP listener synchronously and exposes the
bound address via Addr(), so the e2e smoke can bind to 127.0.0.1:0 and
discover the kernel-assigned port.

Adds an end-to-end smoke test that drives the real steward graph
(in-memory SQLite, real loopback listener, forward-auth) through ingest +
sessions list/detail for two users with the same composite session key,
proving owner isolation reaches all the way through the trust boundary.

Deletes internal/platform/health/steward_unwind_test.go: the canary's
purpose was to surface the unwind gap so Phase 9 could compensate, which
it now does.

README updated with consolidated curl quickstart (forward-auth + OIDC
bearer variants), trust-chain diagram and the proxy-must-strip-Remote-*
spoofing note, response-shape documentation for the API surface, and an
operational notes section covering health, metrics, lifecycle and logs.

feat(session): list and detail JSON API with filters

feat(ingest): NDJSON ingest with chunked transactions and partial-accept

feat(auth): forward-auth + OIDC bearer middleware with shared allowlist

feat(http): chi server with middleware stack + RFC 7807 problem renderer

feat(platform): scribe logger, prometheus registry, health checker set

feat(db): SQLite schema with FTS5 + migration runner

feat(config): viper-loaded config with fail-fast validation

feat: bootstrap lethe server skeleton + wire contract

docs: add lethe task specs (server, collector, search)