feat: ScenarioBranch facade + LF integration mapping v1 - #265

…1GDZ7W6k75paRxBznbZXV4t

Follow-up to the toolchain commit on this branch, from the same measurement.
No workflow here runs `--workspace` or `--all`; every gate names one crate by
path. So `[workspace] members` gates nothing, and ELEVEN of 25 members were in
no job. Two of them (catalog, planner) are deps of lance-graph, so their libs
compiled inside a gated build while their tests ran nowhere; the rest compiled
nowhere at all. That is how `lance-graph-hydrate` reached `main` un-compiling —
`object_store 0.13.2`, a semver-compatible release already in the lockfile,
moved `get`/`put` onto `ObjectStoreExt`, and nothing could see it.

Every step added here was RUN LOCALLY on the pinned 1.97.1 first, and the count
in each comment is what it returned. Nothing is armed on hope:

    catalog 12+15 · planner 368+4 · ontology 276+2+6 · rbac 23 · archetype 16
    consumer-conformance 8 · sigma-tier-router 20 · neural-debug 11
    cognitive-shader-driver 107+2 · hydrate 33

`lance-graph-benches` gets `cargo check --benches` instead of `cargo test`: it
is a benches-only crate with one `harness = false` target, so `cargo test` runs
zero tests and would be a gate that cannot fail. Same shape build.yml already
uses for lance-graph's own benches.

Formatting gates for the same ten. Nine were already rustfmt-clean and simply
had nothing holding them there; `sigma-tier-router` was NOT — 14 hunks in one
file, formatted here, rustfmt output only, its 20 tests unchanged.

Two things this deliberately does NOT do:

- No clippy gates for these crates. Not measured crate-by-crate, and
  `causal-edge` alone already carries 7 pre-existing findings
  (ISS-CAUSAL-EDGE-CARRIES-SEVEN-PRE-EXISTING-CLIPPY-FINDINGS). Arming a lint
  gate on unmeasured crates fails PRs for defects they did not introduce.
- No `--workspace` job. That would catch every FUTURE member automatically and
  is the better long-run answer, but it is a scope and cost decision, not a
  repair. This closes the measured gap; the standing choice stays open.

Also here, because a PR that adds a gate must leave CI green: the two-line
`ObjectStoreExt` import that makes `lance-graph-hydrate` compile, its rustfmt
pass (4 files), and its live `trim_split_whitespace` clippy warning. Those same
fixes ride with the crate's own PR (claude/hydrate-from-zip) — identical hunks,
so a rebase after this merges drops them cleanly. Without them the hydrate gate
added here would be red on arrival.

Cargo.lock is NOT in this commit. It gained one line (`blake3`) from advancing
the OGAR sibling checkout #265 → #279, which is a deliberate dependency bump
and not part of a CI change.

Verified: all seven workflows parse under `yaml.safe_load`, and every one of
the 25 workspace members now resolves to at least one job.

Background: EPIPHANIES E-THE-GATE-IS-A-HAND-MAINTAINED-ALLOWLIST-NOT-THE-WORKSPACE-1
and ISSUES ISS-CI-GATE-IS-AN-ALLOWLIST-NINE-MEMBERS-UNGATED, both landing with
claude/hydrate-from-zip.