fix(model-config-import): stop routing pi providers through cc-switch snapshot

[vastsa]

Fixes #588.

What broke

scanModelConfigs treated CC Switch's providers table as the authoritative index for every downstream tool it supports, pi included. But pi has its own native config at ~/.pi/agent/models.json, and CC Switch only holds a one-shot v18 migration snapshot of it — subsequent edits to models.json never flow back. Our importer dedupe key compares (baseUrl, apiStyle, secret) and skips the pi native draft when the same triplet is already in the cc-switch pile, so the fuller pi draft gets silently filtered out and the stale snapshot wins.

Concrete symptom the reporter observed on 0.15.0:

• opencode-go came in with 9 of 10 models (the default deepseek-flash was dropped).
• deepseek came in missing two models.
• Pi providers surfaced under the "CC Switch" group with the snapshot's renamed label (OpenCode Zen Go instead of opencode-go).
• Nothing showed up in "skipped M" counts, nothing in runtime.log — the models silently disappeared. Root cause matches the issue's own analysis.

Fix

parseCcSwitchProvider now returns [] for app_type='pi'. The pi scanner keeps ownership of ~/.pi/agent/models.json, which is upstream of the cc-switch snapshot. This is the "minimum cost" fix the reporter suggested — it fixes both the silent model loss and the source/name mislabelling at once, without touching the dedupe key or the scan ordering that other appTypes rely on.

If ~/.pi/agent/models.json doesn't exist locally, the pi scanner returns nothing and the cc-switch snapshot is no longer resurrected. That matches how every other source behaves when its native config is missing; the cc-switch snapshot was never a fresh copy anyway.

Tests

• packages/shared/src/model-config-import.test.ts: new regression test — parseCcSwitchProviders skips app_type='pi' rows even when they carry a plausible model list.
• apps/desktop/test/model-config-import.test.mjs: new integration test — reproduces the reporter's setup (cc-switch DB row with 9 models + models.json with 10) and asserts the pi source keeps 10 models and no draft lands under cc-switch.

Verification run in the task worktree:

• pnpm build:js — passes
• pnpm --filter @pi-desktop/shared test — 392 pass (including the new case)
• pnpm --filter @pi-desktop/desktop typecheck — passes
• node --test apps/desktop/test/model-config-import.test.mjs — 5 pass (including the new case)

Not run to green: pnpm lint and the broader pnpm --filter @pi-desktop/desktop test fail on unrelated pre-existing issues (work-panel.test.mjs asserts a minWidth: windowMinWidth string that isn't in apps/desktop/electron/main/index.ts; several CSS token violations under apps/desktop/src/styles/). Both reproduce on unmodified origin/main and are outside this fix's scope.

Compatibility

• No public API, IPC, or SDK change.
• No persisted-state change. Users who already imported the stale cc-switch snapshot must re-run "Import → Model config" to pick up the fuller models.json (this issue is about import; existing DB rows are not migrated).
• User-visible: pi providers now land under the "Pi" group in the import panel with models.json's own name, instead of the CC Switch group with the snapshot's name.

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