Add Pi coding agent CLI/TUI providers and review runner

[atomantic]

Summary

Adds disabled Pi CLI/TUI presets, runtime installation and model discovery, and provider dispatch with positional prompt delivery and thinking-effort controls. Migration 354 adds the presets without replacing local configuration or starting provider work.

Pi is available in reviewer configuration and the slashdo review/enhancement workflows. Public no-tool review discards configured arguments and disables tools, extensions, project trust, and resource discovery. Pi does not advertise an action-review posture.

Closes #6350

Test plan

• 595 focused server tests passed; one platform-specific test skipped.
• 316 client provider and reviewer-picker tests passed.
• Client lint and production build passed.
• 144 slashdo review-contract, transformer, and command-structure tests passed.
• Verified CLI and model-table conventions against Pi's official usage documentation and catalog source; no live model invocation or installation performed.

Claude reviewed both diffs at low effort. Confirmed findings were fixed; 250 server tests and 143 slashdo tests passed after those fixes. Pi isolation flags were verified against the official CLI reference.

Slashdo dependency: atomantic/slashdo#249.

CI follow-up: wired Pi into the shared reviewer model picker and deferred catalog/version parser imports. The import guard now pins the deferred boundary and restores its documented allowance for ordinary module growth; 165 focused server tests passed after that change.

[atomantic]

Leaving this PR open after the configured three CI repair rounds. It has not been merged.

The latest head is 5577499b03d8dd73d1fee3054ced392b3b1e1dbb. CI run https://github.com/atomantic/PortOS/actions/runs/34002884226 failed in server/services/harnesses.test.js:81: the explicit list of shipped records eligible for harness refresh omits the newly supported pi-cli and pi-tui records. The actual result includes both. Update that expected catalog and rerun the required CI Gate before merging; the fail-fast cancellation means the remaining client and Windows jobs are not verified.

Server shard 2 and the database job passed on this head. Local validation includes 595 initial focused server tests, 316 provider/picker client tests, 219 reviewer server tests, 115 reviewer UI tests, client lint/build, and the targeted import checks. Claude reviewed at low effort; confirmed findings were addressed.

The slashdo dependency is already merged: atomantic/slashdo#249. The claim/issue-6350 branch, open PR, assignee, and in-progress marker are retained for pickup. The claim worktree is being removed as prescribed by the CI-stuck handoff procedure.