feat(cli): implement cougr doctor toolchain diagnostics (#247)

[khaylebfortune]

Summary

Implements the cougr doctor subcommand per issue #247 (part of epic #238). Introduces a new cougr-cli workspace subcrate that publishes as cougr-cli on crates.io and exposes the cougr binary. Closes #247.

In scope (per #247 DoD)

Check	What it does	Failure mode message
rust toolchain	parses rustc --version, compares against the rust-version field of the nearest workspace Cargo.toml (stops at first [workspace] manifest)	rustup update stable
wasm32v1-none target	parses rustup target list --installed, exact line match	rustup target add wasm32v1-none
cargo	sanity probe of cargo --version (rustup-managed, no separate version floor)	install Rust via rustup
stellar CLI	parses stellar --version, compares against --stellar-min (default 21.0.0)	install from https://developers.stellar.org/docs/tools/cli/install (with min version in the message)

• All failures print the exact command or install link to fix them, not a generic "missing".
• Summary line N/M checks passed. and a non-zero exit code when any check fails.
• cougr new <name> invokes cougr doctor non-fatally on first run: prints warnings to stderr but the scaffold itself proceeds. Successful scaffold + doctor warnings returns CliError::DoctorWarningsPrinted(0) (exit 0). Scaffold failures keep exit 1. --no-doctor flag suppresses the pre-flight entirely.

Definition of Done evidence

• All checks passing on a correct env -> exit 0: see integration test all_passing_runner_drives_a_clean_report and unit tests pass_when_* in internal/cougr-cli/src/doctor/checks/{rust_toolchain,cargo}.rs.
• Missing wasm32v1-none target -> exact fix rustup target add wasm32v1-none: enforced by wasm32v1_target::check::fail_when_target_missing and missing_wasm_target_prints_specific_fix_command integration test (asserts the literal rustup target add substring and the canonical target constant).
• No stellar CLI on PATH -> install link, not generic not-found: enforced by stellar_cli::check::fail_when_stellar_missing (asserts the fix message includes the official install URL and the configured min version).

Architecture

• doctor::run returns a doctor::Report and is split from doctor::print_report so check logic is unit-testable via the CommandRunner trait. SystemRunner shells out for real; MockRunner registers canned (program, args) -> CommandOutput and returns CommandOutput::missing() (status=-1) for any unmocked call so missing-binary branches are reachable from tests.
• parse_dotted_version rejects pre-release / build-metadata suffixes; rustc 1.85.0-nightly is not treated as [1, 85, 0]. This catches a real footgun: users on a nightly toolchain currently could satisfy a stable 1.70.0 minimum in the old strip-prefix approach.
• resolve_min_rust_version walks up to the first manifest with a [workspace] table, matching the issue's "Root Cargo.toml is the source of truth" wording.
• Pure-std host binary (no no_std, no soroban-sdk); clap-derive for parsing. Depends only on clap.

Tests

• 13 unit-test modules inside check functions and doctor::mod.
• Two integration test files in internal/cougr-cli/tests/:
  • integration_cli.rs: argv parsing, missing-subcommand usage, --help clap short-circuit.
  • integration_doctor.rs: full cougr doctor orchestrator with MockRunner covering all four DoD scenarios + a smoke test against SystemRunner that asserts the rust toolchain check passes on the host binary (locks the contract for cargo install cougr-cli users).
• Per-check unit tests explicitly register CommandOutput::missing() so a future MockRunner refactor cannot silently regress the missing-binary branches.

Why this is in the same repository (and not a fork per docs/strategy/10-repository-strategy.md)

Adding cougr-cli to the same workspace, rather than a separate repository, follows the same logic: the CLI's cougr new/cougr add commands read directly from the example catalog and EXAMPLE_STANDARD.md conventions living in this repository.

The CLI is published as cougr-cli (one binary, cougr), version-locked to cougr-core at 1.1.0.

Out of scope (per #247)

• Auto-installing missing tools.
• Soroban RPC / network connectivity.
• The full cougr new template-driven scaffolder (--template starter|turn-based|hidden-info|session-auth) -- tracked under epic Epic: ship the cougr CLI (new / add / check / doctor) #238 alongside the future cougr add and cougr check subcommands.

Closes #247

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[salazarsebas]

Solid implementation of #247 — looks like the stronger of the two competing doctor PRs (see #279, which has a couple of gaps against the DoD). It currently lives at internal/cougr-cli/; once #288 merges and fixes cli/ as the canonical location for the CLI crate, could you move this there and rebase before we merge?

[salazarsebas]

This targets the same issue as #279 (#247) but with a different approach (internal/cougr-cli/ vs the existing cli/ crate). Since cli/ is already the CLI scaffold on main (with cougr new working), could you rebase onto main and reimplement doctor as a subcommand there? Would also help to coordinate with #279's author since you're both solving #247.

[khaylebfortune]

@salazarsebas I've fix the CI issue. Please kindly check and merge.