…lidation (#36)

Follow-up to the `rig config set --global` isolation gate (#20). Multi-model review
flagged that the `agent_tools_source is None` early return — the branch that lets a global
config legitimately defer its checkout to per-repo/env without a spurious catalog scan —
had no test. Add one: a `--global` set of a non-catalog key, with a global file that pins
no own `agent_tools_source`, must succeed and skip the isolated catalog scan (TDD-verified:
drop the guard and the deferring config is wrongly rejected).

Also fold in the review's small cleanups: trim the duplicated call-site comment (the why
lives in the helper docstring) and drop a stray `(codex P2)` triage tag from a test comment.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

…ed by #34's wizard rebase) (#40)

PR #34 (the `rig setup` wizard, merged as f054910) rebased over main's PR #20
(`rig config get|set`, 635eaf5) and kept the wizard's schema-key config CLI while
deleting #20's dot-path CLI (cmd_config + helpers + parser + tests/test_config_getset.py).
Only one `config` command can register, so the user-facing single-key editor
regressed from the dot-path design to a schema-key one. This restores #20's
dot-path CLI as the user-facing command, coexisting with the wizard.

`rig config get|set` (restored, #20's design):
- get <dot.path> [--global] [--json]: reads ONE nested key from the single target
  file (./rig.yaml, or ~/.config/rig/config.yaml with --global) — NOT the cascade.
  Missing file / absent path exits non-zero; a mapping/list subtree prints as YAML;
  --json emits the JSON value; diagnostics go to stderr.
- set <dot.path> <value> [--global] [--no-apply]: conservative coercion
  (true/false/int/float/null; leading-zero, 1e3, nan/inf, underscored, Unicode
  digits stay strings), creates intermediate mappings, two pre-apply gates
  (schema.validate, then a catalog-backed plan build), rolls the file back on any
  failure, reconciles via the same engine as `rig apply`; --no-apply writes + prints
  the plan only. A repo-local set refuses when ./rig.yaml is absent. Setting the
  removed `scope` key is refused.

The dot-path engine (split_path/get_path/set_path/coerce_scalar/read_yaml_file) was
never deleted — #34 left it in riglib/config.py — so this restores only the CLI
front-end (cmd_config + _cmd_config_get/_cmd_config_set + _config_target/
_read_target_yaml + the argparse wiring) plus tests/test_config_getset.py. The
shared helpers (_load_plan/_print_plan/_print_results/_validate_layer_in_isolation/
_fmt_scalar) already existed identically in main.

The wizard stays as `rig setup`. Its schema-key engine (owning-layer routing,
effective_value, coerce, version-seeding) is internal to the wizard
(setup_wizard.py/schema.py) and is not the `config get|set` command. The wizard
reads/writes config via its own helpers, so dropping main's schema-based cmd_config
breaks nothing in it. Removed the now-orphaned _fmt_config_value (its sole caller
was the replaced cmd_config; #20 uses the identical _fmt_scalar). schema.option_for_key
is now unreferenced in production but kept (public registry API, still tested,
orphaned-by-this-replacement; dead-code rule: investigate, don't delete).

Tests: restored tests/test_config_getset.py (59 tests). Removed the schema-key
`config get|set` CLI tests from tests/test_setup_wizard.py (their CLI surface is
replaced; the schema engine they exercised stays covered by the surviving
test_coerce_*/test_effective_value_*/test_writable_layer_* and the wizard-
interactive tests). Docs reconciled (README, AGENTS.md, docs/config-schema.md);
the wizard's NON_INTERACTIVE_USAGE updated to the dot-path + reconcile framing.
Full suite 800 passed / 8 skipped; smoke OK; gitleaks clean. Live-verified:
get/--json/subtree/--global/--no-apply, coercion edge cases, no-file + scope guards.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>