Add friendly MAC names for connected clients

[vpadman1]

Summary

Tag connected devices with human-readable names so the dashboard shows "Vignesh's iPhone" instead of `AA:BB:CC:DD:EE:FF`.

• aliases.py (new) — load/save/set/remove/resolve helpers backed by `~/.config/wifi-channel-optimizer/aliases.json`. MACs are normalized to uppercase on read and write so lookups don't depend on input casing.
• main.py — the CLI becomes a Click group. Running `python main.py` with no subcommand still launches the dashboard (backward compatible). Three new subcommands manage aliases:
  • `main.py alias set `
  • `main.py alias list`
  • `main.py alias remove `
• dashboard.py — `ClientsPanel` gains a "Device" column that shows the friendly name (falling back to raw MAC). Aliases are loaded once at startup.
• tests/test_aliases.py (new) — 14 tests covering normalization, JSON roundtrip, invalid-file handling, mutators, and resolve fallback.
• README.md — documents the alias subcommands.

Test plan

• `uv run pytest -v` — 43/43 passing (29 existing + 14 new)
• `uvx ruff check .` — clean
• CI green
• `python main.py alias set AA:BB:CC:DD:EE:FF "test"` — roundtrip a real alias