feat(edge-registry): ADR-102 — surface Cognitum cog catalog via /api/v1/edge/registry (#648)

* feat(edge-registry): ADR-102 — surface Cognitum cog catalog via /api/v1/edge/registry

Adds a new sensing-server endpoint that fetches and caches the canonical
Cognitum app registry at
https://storage.googleapis.com/cognitum-apps/app-registry.json (105 cogs
across 11 categories as of v2.1.0). RuView previously had no live
awareness of the catalog — the README's capability table was hand-
curated and went stale as Cognitum shipped new cogs (the registry was
last updated 6 days ago).

ADR:
* docs/adr/ADR-102-edge-module-registry.md — full design, response
  shape, configuration flags, failure modes, and a 12-row security
  review covering SSRF, response inflation, ?refresh abuse, stale-serve
  semantics, TLS, cache poisoning, JSON-panic resistance, etc.

Code:
* v2/.../edge_registry.rs — EdgeRegistry struct + UreqFetcher +
  MockFetcher trait + 7 unit tests. RwLock<Option<CachedEntry>> with
  stale-on-error fallback. MAX_PAYLOAD_BYTES=8 MiB, 10s wire timeout.
* v2/.../main.rs — constructs Option<Arc<EdgeRegistry>> at startup,
  registers GET /api/v1/edge/registry handler, wires Extension layer.
  Handler runs the blocking ureq fetch via tokio::task::spawn_blocking
  so the async runtime stays free.
* v2/.../cli.rs / main.rs Args — three new flags (per user request to
  "allow the registry to be disabled or changed"):
    --edge-registry-url <URL>       (env RUVIEW_EDGE_REGISTRY_URL)
    --edge-registry-ttl-secs <N>    (env RUVIEW_EDGE_REGISTRY_TTL_SECS)
    --no-edge-registry              (env RUVIEW_NO_EDGE_REGISTRY)
  When --no-edge-registry is set or the URL is empty, the endpoint
  returns 404.

Cargo.toml: adds ureq (rustls), sha2, thiserror as direct deps.

README:
* New collapsed "🧩 Edge Module Catalog" section with the full 105-cog
  table generated from the registry, grouped by category with practical
  one-line descriptions (e.g. "Spots irregular heartbeats and abnormal
  heart rhythms", "Detects walking problems and scores fall risk").
  Links to https://seed.cognitum.one/store and the local appliance
  /cogs page. Sits between the HF model section and How It Works.

Tests (7/7 pass):
  first_call_hits_upstream_and_caches
  ttl_expiry_triggers_refetch
  force_refresh_bypasses_fresh_cache
  stale_serve_on_upstream_failure_after_cached_success
  no_cache_no_upstream_returns_error
  upstream_invalid_json_is_treated_as_error
  upstream_sha256_is_deterministic

Security highlights (full review in ADR-102 §"Security review"):
- The registry is metadata-only; per-cog binary signatures (ADR-100)
  remain the trust root for installs. A compromised registry can
  mislead a human reader but cannot ship malicious binaries.
- 8 MiB cap + 10s timeout + Option<Arc<...>> via Extension layer means
  the endpoint can't be used to exhaust memory or pin tokio threads.
- Stale-on-error responses carry an explicit `stale: true` field so
  upstream outages are visible to consumers rather than silently
  masked.
- Endpoint sits behind the existing RUVIEW_API_TOKEN bearer gate when
  set, otherwise unauthenticated (registry contents are public anyway).

* chore: refresh Cargo.lock for ureq/sha2/thiserror deps added by ADR-102

v2/Cargo.lock

@@ -8441,6 +8441,8 @@ dependencies = [
  "once_cell",
  "rustls 0.23.37",
  "rustls-pki-types",
+ "serde",
+ "serde_json",
  "url",
  "webpki-roots 0.26.11",
 ]
@@ -9158,12 +9160,15 @@ dependencies = [
  "ruvector-mincut",
  "serde",
  "serde_json",
+ "sha2",
  "tempfile",
+ "thiserror 1.0.69",
  "tokio",
  "tower 0.4.13",
  "tower-http",
  "tracing",
  "tracing-subscriber",
+ "ureq 2.12.1",
  "wifi-densepose-signal",
  "wifi-densepose-wifiscan",
 ]