feat(#18): affect.fetch — adopt bifrost 0.10.0 mandatory fetch (D1 prerequisite)

bifrost 0.10.0's _supports_affect_plane (bifrost/affect.py:75-80) now requires a
callable fetch for the affect capability to advertise/dispatch at all (INV-012
strong-or-absent), so an emit-only store 400s on EVERY affect op — repinning past
the affect.fetch release (#12/#13) breaks our shipped affect plane until fetch
exists. Implement affect.fetch as a thin async wrapper over the existing get()
read seam, conformed verbatim to the reference InMemoryAffectStore.fetch:
{"found": False} or {"found": True, "snapshot": <verbatim>}, AffectInvalidArguments
on empty ids, opaque (INV-001 — never reads pad/valence).

This is the forced prerequisite for the #18 D1 composite (build_combined_app),
and a new Worldtree I/O point consumed (affect read-back over bifrost).

- Repin bifrost>=0.8.0 -> >=0.10.0 (uv lock: 0.8.0 -> 0.10.0)
- affect_store.py: add async fetch() over get()
- contract bifrost_affect_provider v1.2: fetch FN block + INV-010 (cap = supported+emit+fetch)
- tests: 3 fetch unit + parity_vs_reference_fetch through dispatch_affect_call
- suite 482 -> 486 green

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "ratatoskr"
-version = "0.17.14"
+version = "0.17.15"
 description = "Worldtree Conversation API debug TUI — multi-pane observability dashboard"
 readme = "README.md"
 requires-python = ">=3.12"
@@ -30,7 +30,7 @@ web = [
 # from the debug TUI. Recipe: bifrost/docs/implementing-a-consumer.md.
 provider = [
     "ratatoskr[web]",       # reuse the starlette + uvicorn ASGI stack
-    "bifrost>=0.8.0",       # consumer engines + library (0.8.0/wire-v0.6: scope_filter split into scope_all (AND) + scope_any (OR/union, #11); 0.7.0/v0.5 added agent_self)
+    "bifrost>=0.10.0",      # consumer engines + library (0.10.0: build_combined_app (#18) + mandatory affect.fetch, strong-or-absent; 0.8.0/wire-v0.6: scope_all/scope_any split (#11); 0.7.0/v0.5: agent_self)
     "jsonschema>=4",        # bifrost runtime dep — envelope validation
     "sqlite-vec>=0.1.6",    # vector index for the memory plane (vec0 virtual table)
 ]