feat(safety): add contextual action review with guarded and observe modes

Introduce a pre-execution safety layer that reviews effectful agent actions
against compiled, frozen evidence before they run.

`--safety-mode guarded` allows non-destructive interaction after review;
`--safety-mode observe` permits passive target interaction only. `off` stays
the default, so existing runs are unchanged.

Deterministic rules decide what they can on their own: destructive commands,
code-loading environment overrides, blocked browser actions, and mutating
requests in observe mode are refused without a model call, and a small set of
read-only commands is allowed outright. Everything else compiles an evidence
packet — command, scope, script source and its local import closure, prior
tool-call evidence, and browser snapshot context — for a bounded reviewer that
may make one isolated inspection call. Incomplete evidence fails closed.

In safety modes, user-owned local directories are copied into the run
directory so the originals are never mounted writable, while `.git`,
`.agents`, and `.codex` inside the copy stay read-only.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/docs.json

@@ -25,6 +25,7 @@
             "pages": [
               "usage/cli",
               "usage/scan-modes",
+              "usage/safety-modes",
               "usage/instructions"
             ]
           },