fix(launcher): retry uv install steps to survive transient first-run 448 (Windows/OneDrive)

[lstein]

Problem

On a Windows machine with OneDrive Files-On-Demand active, the very first run of the launcher aborted with:

error: Failed to create Python minor version link directory
  Caused by: ... untrusted mount point. (os error 448)

After extensive isolation (same uv binary, flags, env, folder, elevation, cwd, and environment all tested), the failure proved to be a transient first-run race: OneDrive's cloud-filter driver (cldflt) briefly returns STATUS_UNTRUSTED_MOUNT_POINT (448) on uv's managed-Python minor-version junction creation while the filter engages the freshly-created folder tree. Re-running the exact same uv command moments later — from bash, cmd, or even the Explorer shortcut — succeeds every time. uv has no flag to skip that junction (ensure_minor_version_link is unconditional and fatal in uv's source), so we can't avoid creating it; we can only survive a one-time failure.

Fix

Wrap the two uv install commands in a short, growing-backoff retry (installStepAttempts = 3, 3s then 6s). A one-time 448 self-heals on the next attempt instead of hard-aborting the user's first run — the moment it actually bites. Retrying is cheap: uv caches downloads, so a retry reuses the already-fetched Python/wheels. The retry logic is factored into a pure, unit-tested withRetry(attempts, backoff, fn) helper.

Also pass --no-bin to uv python install so uv stops dropping a python3.12.exe shim into the user's ~/.local/bin (which it can't manage on reinstall, and is one more cross-folder write outside our self-contained runtime root). The launcher runs start_photomap from the tool venv directly and never needs Python on PATH.

Tests

• withRetry: recovers after transient failures, returns the last error when exhausted, stops on first success (no backoff). Pure helper — no real uv spawned.
• go build, go vet, go test, gofmt -l all clean.

Notes

• Independent of fix(launcher): force uv to use managed Python (avoids macOS Xcode prompt) #322 (the macOS only-managed fix), which is already merged.
• The retry is a best-effort mitigation for a heisenbug we can't reproduce on demand; it does not change behavior on the happy path (single attempt, no delay).

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