Retire work_products whose files the run deleted

Fix #16 kept deletions from registering, but rows created by earlier
runs stayed `status = "active"` forever even after the agent `rm`'d
the file. The DocumentCenter kept showing zombies and
`openWorkProduct` resolved to an empty path.

`ChangeSet` now carries both `changed` and `deleted` paths, populated
from the two detectors:

  - git porcelain: the `D` status entries that were previously
    dropped are now captured into `deleted` instead;
  - baseline diff: paths present in the baseline but no longer on
    disk at diff time are `deleted`.

A new `retireDeletedArtifacts` pass runs alongside
`projectChangedPaths` and flips the matching
`work_products.status` to `archived`, bumping `last_touched_by_run_id`
to the retiring run so the provenance timeline records the deletion.
`upsertFilesystemArtifact` sets `status = "active"` on update so a
subsequent run that recreates the path brings the row back into the
visible set. A new `ProjectionOutcome` variant — `retired` — lets the
hook and reconciliation logs report both sides of the fan-out.

src/main/agent-runtime/hook-handlers.ts

@@ -194,9 +194,10 @@ export function handleAfterToolCall(
       },
     );
     const registered = outcomes.filter((o) => o.kind === "inserted" || o.kind === "updated").length;
-    if (registered > 0) {
+    const retired = outcomes.filter((o) => o.kind === "retired").length;
+    if (registered > 0 || retired > 0) {
       deps.logger.info(
-        `[hook-handlers] projection registered ${registered} artifact(s) for run ${ctx.runId} via ${payload.toolName}`,
+        `[hook-handlers] projection for run ${ctx.runId} via ${payload.toolName}: ${registered} registered, ${retired} retired`,
       );
     }
   } catch (error) {