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/runtime-bridge.ts

@@ -133,9 +133,10 @@ export class RuntimeBridge {
         workspaceBaseline: ctx.workspaceBaseline,
       });
       const inserted = outcomes.filter((o) => o.kind === "inserted").length;
-      if (inserted > 0) {
+      const retired = outcomes.filter((o) => o.kind === "retired").length;
+      if (inserted > 0 || retired > 0) {
         this.deps.logger.info(
-          `[runtime-bridge] reconciliation registered ${inserted} new artifact(s) for run ${ctx.runId}`,
+          `[runtime-bridge] reconciliation for run ${ctx.runId}: ${inserted} registered, ${retired} retired`,
         );
       }
     } catch (error) {