fix(delta): drop delta from default features (CI green)

Real CI failure root cause: `deltalake 0.32` removed
`delta_datafusion::DeltaTableProvider::try_new`; the new API is
`TableProviderBuilder::new().with_snapshot(...).with_log_store(...).build().await`
(async, fallible). `crates/lance-graph/src/table_readers.rs:119`
still calls the old API and fails to compile under default features.

Per codex P1's explicit fallback option ("disable/remove the Delta
reader until it can be aligned"), drop `delta` from
`crates/lance-graph/Cargo.toml :: default = [...]`. The `delta`
feature remains opt-in via `--features delta` for any caller that
wants to patch up the broken state themselves; `DeltaTableReader`
itself is already `#[cfg(feature = "delta")]` so non-default builds
don't even compile the broken file. Refactor to TableProviderBuilder
is queued as a follow-up — `TODO(lance-bump-delta)` left at the
feature definition with the new API surface noted.

Local `cargo build --manifest-path crates/lance-graph/Cargo.toml`
(matches CI command) finishes clean in 5m16s.

Author: claude

crates/lance-graph/Cargo.toml

@@ -61,8 +61,14 @@ bgz17 = { path = "../bgz17", optional = true }
 bgz-tensor = { path = "../bgz-tensor", optional = true }
 
 [features]
-default = ["unity-catalog", "delta", "ndarray-hpc", "planner", "bgz17-codec", "tensor-codec"]
+default = ["unity-catalog", "ndarray-hpc", "planner", "bgz17-codec", "tensor-codec"]
 unity-catalog = ["lance-graph-catalog/unity-catalog"]
+# TODO(lance-bump-delta): deltalake 0.32 removed `DeltaTableProvider::try_new`;
+# new API is `TableProviderBuilder::new().with_snapshot(...).with_log_store(...).build().await`.
+# Refactor `table_readers.rs::DeltaTableReader` to the new builder API in a
+# follow-up PR. Dropped from `default` features for now so CI stays green on
+# the lance/lancedb bump; still opt-in via `--features delta` if a caller
+# accepts the broken state.
 delta = ["dep:deltalake", "dep:url"]
 # lancedb: high-level table/connection API (Python/JS SDK equivalent in Rust).
 # Enables LanceDB-compatible connection strings, table management, and the