feat(cli): thread Config through the import path

[ecalifornica]

Part of #184 (PR 6 of the plan there). Stacked on #197. path-cli only.

What

• cmd_p passes &Config to cmd_import::run in the Import arm. p derive reuses cmd_import::run and is not threaded; it loads a transitional Config at its call site.
• cmd_import constructs every conversation provider via with_resolver(providers::*_resolver(config)). The git, github, and pathbase arms construct no conversation provider and do not change.
• The pi arm chains with_sessions_dir when --base is given, so --base wins over the injected home.
• The derive.rs single-session helpers (derive_claude_session and siblings) take &Config and build their managers from the same resolver functions.
• record_artifact and record_is_current in the sync engine take &Config. The transitional per-call loads inside them are gone.
• cmd_share is threaded by its own PR. Its two forced call sites (derive_session, and the record_artifact call in share_explicit) load a transitional Config. A load failure at the record_artifact site degrades like a manifest-write failure.
• HarnessBundle::from_environment() stays: share still uses it, and the import path never constructs a bundle.

Emscripten

• cmd_import compiles on emscripten. Its claude/gemini/codex/copilot/pi arms construct providers there from the ungated resolvers.
• The opencode and cursor arms bail inside their #[cfg(target_os = "emscripten")] blocks before any construction; opencode_resolver and cursor_resolver keep their #[cfg(not(target_os = "emscripten"))] gates, and so do the matching derive.rs helpers.
• emit uses config only in its native manifest-record calls; it carries expect(unused_variables) on emscripten.

Behavior change

• p import pi / p derive pi / share of a pi session, Windows only: the CLI injects Config::home_dir(), which falls back to $USERPROFILE. The pi resolver's internal lookup reads $HOME only (pi: resolver home lookup ignores $USERPROFILE #192). With $HOME unset, these resolve %USERPROFILE%\.pi\agent\sessions.

Tests

• The engine tests pass the jail Config to record_artifact; no engine test reads the ambient environment for it.
• The p import integration tests run the binary under ScopedHome, so $HOME reaches the resolvers through Config end to end (import_copilot_writes_cache, import_records_manifest_so_sync_skips).
• The cmd_import unit tests build managers from injected resolvers and call the *_with_manager helpers directly; the signature changes do not touch them.

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[github-actions]

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[ecalifornica]

cmd_p already holds &Config, so cmd_derive::run could take it today. Leaving the transitional load in: it carries the same marker as the other unthreaded sites and gets swept with them.