feat: board add accepts probe-rs selector strings - #10

Summary

paavo-cli board add --probe now accepts probe-rs selector strings directly — either a bare token (1fc9:0143-0:SERIAL) or a full pasted probe-rs list line — instead of the brittle split(':') that mis-parsed probe-rs's -IFACE suffix and truncated colon-bearing serials. Selectors are parsed and validated at registration (fail fast, not hours later at probe_attach) via a canonical ProbeSelector::parse in paavo-proto; the USB interface index is preserved and threaded to probe-rs at attach; and VID/PID are stored canonicalized (lowercase 4-hex) by both ingestion paths.

Feature

• paavo-proto: optional ProbeSelector.interface; ProbeSelector::parse (token or list line, probe-rs grammar incl. colon-serials), validate, canonicalize; typed ProbeSelectorParseError.
• paavo-cli: board add parses via proto and fails locally before any network call; reworded --probe help.
• paavod: POST /boards canonicalizes + validates (400 on bad hex); boards.toml seeds canonicalized + validated at startup.
• paavo-probe: honors interface at probe attach (e.g. FTDI multi-interface).

Deployment fixes (contrib)

Real landmines hit bringing up a fresh lab box:

• paavod.service: set CARGO_HOME/RUSTUP_HOME/PATH to the state dir so the sandboxed daemon (ProtectHome=true) can actually build test crates.
• 99-probes.rules: add NXP MCU-Link (1fc9); group probes to the paavo service user; document an all-USB catch-all.
• contrib/README.md: install the toolchain into the state dir.
• docs: corrected the boards.toml description; added an AGENTS.md landmine.

Design docs

• Spec: docs/superpowers/specs/2026-06-29-probe-selector-parsing-design.md
• Plan: docs/superpowers/plans/2026-06-29-probe-selector-parsing.md

Test plan

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace — new proto parse/canonicalize unit tests, CLI fail-fast + end-to-end pasted-list-line round-trip, daemon 400 + normalize-on-store tests, boards.toml startup validate/canonicalize tests
• Hardware (PAAVO_HW=1): interface threading on a real MCX-A266 probe