cleanup: drop workspace warnings from 11 to 6

Three trivial cleanups that pull the workspace baseline down by five:

  - vectord/trial.rs: removed unused ObjectStore import (not referenced
    anywhere in the file; cargo's unused_imports lint was flagging it
    on every check). Net: -2 warnings (cascade effect from one import).
  - ui/main.rs:1241: `Err(e)` with unused binding → `Err(_)`.
  - ui/main.rs:1247: `let mut import_table` never mutated → `let`.

Matters because the scrum_applier's hardened warning-count gate uses
this baseline as its reject threshold. Lower baseline = lower floor
= any future patch that adds a warning trips the gate earlier.

Remaining 6 warnings are all aibridge context::estimate_tokens
deprecation notices pointing at a planned-but-unbuilt
shared::model_matrix::ModelMatrix::estimate_tokens. Fix requires
creating that type (next commit).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/ui/src/main.rs

@@ -1238,13 +1238,13 @@ fn IngestPanel() -> Element {
                         pg_tables.set(Some(tables));
                     }
                 }
-                Err(e) => pg_tables.set(None),
+                Err(_) => pg_tables.set(None),
             }
             pg_loading.set(false);
         });
     };
 
-    let mut import_table = move |table: String| {
+    let import_table = move |table: String| {
         let host = pg_host.read().clone();
         let db = pg_db.read().clone();
         spawn(async move {

crates/vectord/src/trial.rs

@@ -10,7 +10,6 @@
 /// JSONL on every event. See `append_log.rs` for the full rationale.
 
 use chrono::{DateTime, Utc};
-use object_store::ObjectStore;
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::sync::Arc;