Give agents hands: workspace read/list/exec tools so engineers build instead of describing

Every "engineering" deliverable the company ever produced was a markdown
skeleton, because documentation was the ceiling of the toolset:
write_deliverable and create_document were the only artifact tools. An
engineer could not see the files that exist, read a line of code, or run a
single command — and create_task hardcoded requires_filesystem to false, so
the entire approval-gated read_write mount plumbing was dead code.

New workspace capability (agent-workspace-tools.ts):
- list_files / read_file: explore the bound workspace, traversal-guarded by
  the same resolveWorkspacePath used for writes, size- and count-capped.
- run_command: real shell execution with the workspace as cwd, 120s timeout,
  16k output cap. Gated on the task's approved filesystem grant — the same
  requires_filesystem flag that flips the mount to read_write and routes the
  task through operator approval (auto-approved only in AI-CEO mode, which
  is that mode's explicit contract).
- create_task now takes requires_filesystem, so the CEO and officers can
  delegate engineering work that is allowed to change code and run tests.
- Prompts brief every agent on the tools, and filesystem tasks state the
  bar directly: real output is code that builds and tests that pass — a
  document describing the work does not close an engineering task.

Tests: tool registry, dependency-folder-skipping listing, traversal refusal,
the run_command access gate plus exit-code reporting, and the create_task
approval path for filesystem work.

tests/unit/execution-modes.test.ts

@@ -54,7 +54,7 @@ function harness(mode: "ai_ceo" | "ai_cofounder"): Harness {
       agent: { id: ceoId, modelProviderId: null, modelId: null },
       taskProjectId: null,
       taskGoalId: null,
-      workspace: { id: workspaceId, localPath: workspaceRoot },
+      workspace: { id: workspaceId, localPath: workspaceRoot, writeAccess: true },
     },
     deps: { db: connection.db, organization, chat: new ChatService(connection.db) },
   };