Add per-project sandbox mode and Bedrock service-tier

Sandbox mode: new per-project toggle that turns on Claude Code's bash
sandbox inside the container. Adds `bubblewrap` and `socat` to the
Dockerfile (the two Linux deps required by the sandbox), and emits a
managed `sandbox` block into `~/.claude/settings.json` via the existing
CLAUDE_CODE_SETTINGS_JSON entrypoint merge:

- `enabled` mirrors the Triple-C toggle and is always emitted, so the
  entrypoint's recursive jq merge clears any prior on-state from the
  persisted named volume — Triple-C is authoritative.
- `enableWeakerNestedSandbox: true` because we run inside Docker without
  privileged user namespaces.
- `allowUnsandboxedCommands: false` to disable the `dangerouslyDisableSandbox`
  escape hatch — opting into the sandbox shouldn't come with a runtime
  bypass.

When sandbox is on, a SANDBOX_INSTRUCTIONS section is appended to
CLAUDE_INSTRUCTIONS so Claude can guide users through allowing extra
paths/domains, excluding `docker *`/`watchman *` from the sandbox, and
the rule that `sandbox.enabled` is owned by Triple-C. The Claude-Code
settings fingerprint includes sandbox state (only when on, to avoid
spuriously flagging existing containers for recreation on upgrade).

Bedrock service tier: new optional field on the per-project Bedrock
config. When set, exported as ANTHROPIC_BEDROCK_SERVICE_TIER (added in
Claude Code 2.1.122) and included in the Bedrock fingerprint.

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

container/Dockerfile

@@ -31,6 +31,8 @@ RUN for i in 1 2 3 4 5; do \
     pkg-config \
     libssl-dev \
     cron \
+    bubblewrap \
+    socat \
     && rm -rf /var/lib/apt/lists/*
 
 # Remove default ubuntu user to free UID 1000 for host-user remapping