refactor(cli): unify wire path through TelepathClient via RttTransport

[tarotene]

Summary

• Add tools/telepath-cli/src/rtt_transport.rs: RttTransport struct that owns Session + Rtt and implements std::io::Read + std::io::Write, bridging probe-rs's &mut Core-per-call API to the trait interface expected by TelepathClient
• Remove inline COBS encode/decode, postcard serialize/deserialize, and 5-second read loop from cmd_ping; replace with TelepathClient::call_raw
• Read::read busy-loops with 1ms sleep until data arrives, preventing read_exact from seeing Ok(0) as EOF; respects a configurable read_deadline (default: 5 seconds)
• drain_debug_logs (RTT ch0 passthrough) moved into RttTransport and called from cmd_ping and the REPL loop via the new TelepathClient::transport_mut() accessor
• Drop direct cobs, telepath-wire deps from telepath-cli/Cargo.toml; add telepath-host path dep

Test plan

• cd tools/telepath-cli && cargo build — clean
• cd tools/telepath-cli && cargo clippy -- -D warnings — clean
• cd tools/telepath-cli && cargo fmt --check — clean
• cargo build --workspace (root) — workspace unaffected; telepath-host re-compiles with transport_mut()
• Hardware: cd examples/nrf52840-dk && cargo run --release then cd tools/telepath-cli && cargo run -- ping → ping -> 0xDEADBEEF

Hardware verification requires nRF52840-DK + J-Link.

Closes #2
References Stage A (A2) in #3

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR refactors telepath-cli to route all RPC traffic through telepath-host::TelepathClient by introducing an RTT Read/Write adapter, eliminating duplicated framing/serde logic in the CLI.

Changes:

• Added RttTransport (owning Session + Rtt) that implements std::io::Read + Write for probe-rs RTT I/O.
• Updated telepath-cli ping and REPL to use TelepathClient::call_raw, plus a transport_mut() accessor to drain RTT debug logs.
• Simplified CLI dependencies by removing direct telepath-wire and cobs usage in favor of telepath-host.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
tools/telepath-cli/src/rtt_transport.rs	Adds RTT adapter implementing Read/Write, deadline handling, and debug log draining.
tools/telepath-cli/src/main.rs	Switches ping + REPL to use TelepathClient over RttTransport; removes inline wire/framing logic.
tools/telepath-cli/Cargo.toml	Drops direct wire/framing deps; adds telepath-host dependency.
crates/telepath-host/src/lib.rs	Adds TelepathClient::transport_mut() for side-channel transport access.

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