feat(cli): thread Config through the export path

[ecalifornica]

Part of #184 (PR 7 of the plan there). Stacked on #198. path-cli only.

What

• cmd_p passes &Config to cmd_export::run, cmd_project::run, and cmd_incept::run. The two forwarders pass it straight to cmd_export::run.
• Every run_<harness> and every write_into_<harness> helper takes &Config. Each one builds its PathResolver from providers::<harness>_resolver(config).
• The pub(crate) project_<harness> wrappers take &Config and forward it.
• cmd_resume::project_into_harness takes &Config. cmd_resume is threaded by its own PR; run_with_strategy loads a transitional Config at that call site.
• The pathbase arm is unchanged. $PATHBASE_URL, the credentials path, and the upload-side reads stay where they are; a later PR owns them.
• The cache store's config_dir() call is unchanged for the same reason.
• Emscripten gating is unchanged: every providers:: call site sits inside an existing #[cfg(not(target_os = "emscripten"))] function, and the bail blocks consume config (verified by reading the cfg attributes; host test/clippy do not compile the wasm target).

Behavior change

• p export pi / p project / p incept / resume 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. This matches the import and sync changes earlier in the series.

Tests

• The cmd_export unit tests inject a Config in place of setting $HOME around each call. Two helpers build them: config_with_home for the harnesses that resolve from the home, and config_with_opencode_home, which also injects xdg_data_home because the opencode resolver's internal $XDG_DATA_HOME read wins against the home.
• Eleven tests drop their $HOME save/restore block and their TEST_ENV_LOCK guard. They no longer serialize against the rest of the suite.
• pathbase_repo_flag_requires_login keeps its $TOOLPATH_CONFIG_DIR scaffolding: the pathbase arm still reads the environment.
• cmd_resume's project_into_harness_claude_round_trip loads a Config inside its scoped-home guard.
• tests/resume.rs runs the projection end to end for all seven harnesses under a ScopedHome, so $HOME reaches the resolvers through Config.

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