Add replay-buffer browser CLI

[ParamThakkar123]

Motivation

• Provide an easy way to inspect HDF5 replay buffers interactively to spot bad data by scrolling episodes and viewing rewards/actions overlaid on observations.
• Keep the CLI lightweight by lazy-loading optional dependencies and offering a summary-only mode when GUI dependencies are unavailable.

Description

• Add a new replay command group and replay browse CLI in tools/cli.py that prints a summary and can launch a local web UI for an HDF5 replay buffer.
• Implement the browser backend in tools/replay_browser.py including HDF5 metadata parsing for flat and per-episode layouts, episode splitting by done flags, and observation/action shape reporting.
• Add PNG frame rendering with reward/action/done overlays and automatic upscaling for small frames in tools/replay_browser.py and serve frames/metadata via a small stdlib HTTP server.
• Update documentation docs/source/cli.md with the new command and optional dependencies, and add tests in tests/test_cli.py covering summary output and PNG rendering with optional-dependency skips.

Testing

• Verified python -m tools.cli replay browse --help prints the new command usage successfully.
• Verified python -m py_compile tools/cli.py tools/replay_browser.py succeeds to ensure syntax is valid.
• Ran pytest -q tests/test_cli.py -q which passed (9 passed, 2 skipped due to optional replay-browser dependencies being unavailable in the test environment).

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Codex Task

[github-actions]

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