Summary

Closes #213.

Adds the resolved TOML config file location to all-smi --help, introduces a strictly read-only all-smi config path subcommand for scripting/discovery, and fills the config-path gap in the man page FILES section.

Before

all-smi --help did not reveal where the config file lives. The only pointer was the --config <PATH> flag description, which redirected to all-smi config init — a command that writes a file as a side effect. A new user had no way, from -h / --help alone, to know a config file even existed or where it would go.

After

• all-smi --help and all-smi -h show a new "Configuration file" section with the resolved per-user path ($HOME / $XDG_CONFIG_HOME / %APPDATA% aware) plus an (active) / (not found) marker.
• all-smi config path [--json] prints the active path + ordered candidate search list with no file writes. The JSON form has a stable schema (active, exists, overridden, search_order).
• --config <PATH> is honoured by config path (reports the override + suppresses the search list).
• Man page FILES enumerates per-platform config.toml paths and points at the new discovery surface.
• README adds config path to the helpers list and tightens the --config flag wording.

Implementation notes

• Dynamic after_help is composed at runtime in cli::build_command_with_runtime_help() because the resolved path embeds the user's $HOME / $XDG_CONFIG_HOME, which a static #[command(after_help = ...)] cannot do.
• main.rs parses via Cli::from_arg_matches so the runtime composition reaches --help.
• Shared paths::format_path_with_existence() keeps the existence marker vocabulary consistent between --help and config path.
• Read-only guarantee for config path is regression-tested (run_path_does_not_create_file).
• No-home-directory case is handled with a clear inline message ((no config path resolvable — set $HOME or $XDG_CONFIG_HOME)).

Files changed

• src/cli.rs — dynamic after_help builder; reworded --config doc.
• src/cli_config.rs — new ConfigAction::Path(ConfigPathArgs).
• src/config_cmd/mod.rs + src/config_cmd/path.rs — read-only runner with text + JSON output.
• src/common/paths.rs — shared existence-marker formatter.
• src/main.rs — parse via Cli::from_arg_matches after runtime composition.
• docs/man/all-smi.1 — config subcommand in COMMANDS; per-platform paths in FILES; ENERGY ACCOUNTING points at config path.
• README.md — config path helper entry; tightened --config wording.
• tests/config_path_help_test.rs (integration) + inline unit tests in paths.rs, cli.rs, config_cmd/path.rs.

Test plan

• cargo fmt --check
• cargo clippy --lib --tests -- -D warnings
• cargo test --test config_path_help_test (7 new integration tests)
• cargo test --lib common::paths::tests (3 new + 7 existing pass)
• cargo test --bin all-smi config_cmd::path (6 new tests pass)
• cargo test --bin all-smi cli::tests (3 new + 5 existing pass)
• cargo test --bin all-smi config_cmd (existing render tests still pass)
• cargo test --test config_file_integration_test (existing 14 tests still pass)
• Manual: ./target/debug/all-smi --help shows Configuration file + Energy Session blocks
• Manual: ./target/debug/all-smi config path prints active path + search order
• Manual: ./target/debug/all-smi config path --json emits stable JSON schema
• Manual: confirmed config path does NOT create the file (no ~/.config/all-smi/ after invocation; no /tmp/explicit_nope.toml after --config override)
• Manual: groff -Tutf8 -man docs/man/all-smi.1 renders cleanly; new FILES entries display correctly